some preferred embodiments of the present disclosure will now be described in reference to the accompanying drawings . explained first is the frame structure of the advanced satellite digital broadcasting system proposed as a next - generation satellite digital broadcasting system in japan . fig3 is a schematic view explanatory of the frame structure of the advanced satellite digital broadcasting system . as illustrated , one frame is composed of 120 modulation slots . in this example , the modulation slots are numbered from # 1 to # 120 . each modulation slot includes 24 symbols for synchronization purposes ( indicated as “ fsync ,” “! fsync ” and “ ssync ” in fig3 ) and 32 known symbols ( each indicated as “ pilot ” in fig3 ) used for determining signal constellation points . also , each modulation slot includes 66 transmitted data items each composed of 136 symbols . for example , the transmitted data items in modulation slot # 1 are indicated as “ data # 1 ” through “ data # 66 ,” and the transmitted data items in modulation slot # 2 are shown as “ data # 67 ” through “ data # 132 .” furthermore , in each modulation slot , a tmcc signal is inserted between every two transmitted data items , the signal being made up of four symbols constituting control information about transmission and multiplexing . in fig3 , reference character t denotes the tmcc signal . each frame of the advanced satellite digital broadcasting system structured as explained above is made up of a total of 1 , 115 , 520 symbols . the advanced satellite digital broadcasting system makes it possible for a plurality of modulation techniques to coexist in each frame . for example , up to eight transmission modes may be defined in a single frame , each transmission mode allowing a different modulation technique to be adopted . with the advanced satellite digital broadcasting system , it is possible to use five modulation techniques consisting of bpsk , qpsk , 8psk , 16apsk , and 32apsk . fig4 is a schematic view showing typical transmission modes in a single frame of the advanced satellite digital broadcasting system . for purpose of simplification , only two transmission modes are defined . as shown in fig4 , transmission mode 1 set for the transmission technique of 32apsk is assigned to modulation slots # 1 through # 40 , and transmission mode 2 for the transmission technique of 16apsk is assigned to modulation slots # 41 through # 120 . the transmission mode of each modulation slot can be identified by analyzing the tmcc signal found two frames earlier than the current frame . the receiver is thus arranged to acquire and retain all tmcc signals inserted in each modulation slot of the frame received two frames earlier . this arrangement allows the receiver to identify the modulation technique for each modulation slot in each frame received . regardless of the transmission mode of each modulation slot , it should be noted , the tmcc signal is typically subjected to π / 2 shift bpsk modulation . the present disclosure aims to search for optimum loop gains even where a plurality of modulation techniques are used in each transmission frame , as shown in fig4 for example . fig5 is a block diagram showing a typical structure of a frequency / phase synchronizing circuit practiced as one embodiment of the present disclosure . the frequency / phase synchronizing circuit shown in fig5 is incorporated in the demodulation circuit 3 of a receiver having the same structure as that indicated in fig1 . the structure of the frequency / phase synchronizing circuit shown in fig5 is largely different from the ordinary circuit structure in the following : that a main pll circuit is supplemented with a sub pll circuit having the same structure , that the loop gains of the loop filters in the main and sub pll circuits are variable , and that a loop gain control setup is additionally provided . the main pll circuit 31 - 1 and the sub pll circuit 31 - 2 are structured in such a manner as to use members that have the same characteristics and to possess the same circuit structure . if the same value is set as the loop gain of the loop filter in each of the main and sub pll circuits 31 - 1 and 31 - 2 and if the same signal is input to the two circuits , then the signal output from the main pll circuit 31 - 1 coincides with the signal output from the sub pll circuit 31 - 2 . as will be explained later , the main pll circuit 31 - 1 is a circuit that actually performs synchronized detection . the sub pll circuit 31 - 2 may be considered a circuit that performs “ trials ” to determine the loop gain defining the characteristics of the loop filter in the main pll circuit 31 - 1 . the reception signal ri , which is the i - th signal ( at the i - th symbol ), is input to a multiplier 41 - 1 of the main pll circuit 31 - 1 , to a multiplier 41 - 2 of the sub pll circuit 31 - 2 , and to a multiplier 32 . the reception signal ri includes the phase error represented by 2πδft + θ as mentioned above . the multiplier 41 - 1 of the main pll circuit 31 - 1 multiplies the reception signal ri by a phase control amount e − j ( 2πδft + θ ) supplied from a numerically controlled oscillator 44 - 1 . a signal d main , i obtained through multiplication is output to a phase error detector 42 - 1 . the signal output from the multiplier 41 - 1 is the same as a synchronized detection signal d main , i that is a phase control signal output from the multiplier 32 . the phase error detector 42 - 1 detects a phase error that may remain in the signal output from the multiplier 41 - 1 , and outputs a main phase error detection value e main , i . the phase error detector 42 - 1 performs phase error detection in the same manner as the phase error detector 22 shown in fig2 . the same holds for a phase error detector 42 - 2 of the sub pll circuit 31 - 2 , to be discussed later . the main phase error detection value e main , i output from the phase error detector 42 - 1 is fed to a multiplier 51 - 1 of a loop filter 43 - 1 . the loop filter 43 - 1 is a proportional integral loop filter that filters the main phase error detection value e main , i output from the phase error detector 42 - 1 . the filtered value is output to the numerically controlled oscillator 44 - 1 . more specifically , the multiplier 51 - 1 of the loop filter 43 - 1 multiplies the main phase error detection value e main , i by g 1 main in accordance with a loop gain g 1 main established by a loop gain control portion 34 . the value obtained through multiplication is output to a multiplier 52 - 1 and an adder 54 - 1 . the multiplier 52 - 1 further multiplies by g 2 the g 1 main - fold main phase error detection value e main , i fed from the multiplier 51 - 1 . the value obtained through multiplication is output to an integrator 53 - 1 . the integrator 53 - 1 integrates the output from the multiplier 52 - 1 and outputs the result of the integration to the adder 54 - 1 . the adder 54 - 1 adds the output from the multiplier 51 - 1 and the output from the integrator 53 - 1 , and outputs the sum of the addition as a filtering result θ main , i to the numerically controlled oscillator 44 - 1 . the numerically controlled oscillator 44 - 1 generates the phase control amount e − j ( 2πδft + θ ) based on the filtering result from the loop filter 43 - 1 , and outputs the generated control amount to the multipliers 41 - 1 and 32 . the multiplier 32 multiplies the reception signal ri by the phase control amount e − j ( 2πδft + θ ) supplied from the numerically controlled oscillator 44 - 1 of the main pll circuit 31 - 1 . the signal obtained through multiplication is output as the synchronized detection signal d main , i . meanwhile , a signal containing the signal d main , i , main phase error detection value e main , i , and filtering result θ main , i is supplied from the main pll circuit 31 - 1 as a main pll intermediate signal to a main pll control error detector 61 of a pll control error comparison portion 33 . the sub pll circuit 31 - 2 also performs the same processing on the same reception signal ri as that input to the main pll circuit 31 - 1 . that is , the multiplier 41 - 2 of the sub pll circuit 31 - 2 multiplies the reception signal ri by the phase control amount e − j ( 2πδft + θ ) supplied from a numerically controlled oscillator 44 - 2 . a signal d sub , i obtained through multiplication is output to a phase error detector 42 - 2 . the phase error detector 42 - 2 detects a phase error that may remain in the signal output from the multiplier 41 - 2 , and outputs a sub phase error detection value e sub , i accordingly . the sub phase error detection value e sub , i output from the phase error detector 42 - 2 is fed to a multiplier 51 - 2 of a loop filter 43 - 2 . the multiplier 51 - 2 of the loop filter 43 - 2 multiplies the sub phase error detection value e sub , i by g 1 sub in accordance with a loop gain g 1 sub established by the loop gain control portion 34 . the value obtained through multiplication is output to a multiplier 52 - 2 and an adder 54 - 2 . for example , the loop gain g 1 sub set for the multiplier 51 - 2 is made different from the loop gain g 1 main set for the multiplier 51 - 1 of the main pll circuit 31 - 1 . the multiplier 52 - 2 further multiplies by g 2 the g 1 sub - fold sub phase error detection value e sub , i fed from the multiplier 51 - 2 . the value obtained through multiplication is output to an integrator 53 - 2 . the multiplier 52 - 1 of the main pll 31 - 1 and the multiplier 52 - 2 of the sub pll circuit 31 - 2 thus perform weighting by use of the same loop gain . the loop gain g 2 is a predetermined fixed value . the integrator 53 - 2 integrates the output from the multiplier 52 - 2 and outputs the result of the integration to the adder 54 - 2 . the adder 54 - 2 adds the output from the multiplier 51 - 2 and the output from the integrator 53 - 2 , and outputs the sum of the addition as a filtering result θ sub , i to the numerically controlled oscillator 44 - 2 . the numerically controlled oscillator 44 - 2 generates the phase control amount e − j ( 2πδft + θ ) based on the filtering result from the loop filter 43 - 2 , and outputs the generated control amount to the multiplier 41 - 2 . meanwhile , a signal containing the signal d main , i , sub phase error detection value e sub , i , and filtering result θ sub , i is supplied from the sub pll circuit 31 - 2 as a sub pll intermediate signal to a sub pll control error detector 62 of the pll control error comparison portion 33 . the main pll control error detector 61 of the pll control error comparison portion 33 receives the main pll intermediate signal fed from the main pll circuit 31 - 1 every time the reception signal ri is input . for example , the main pll control error detector 61 calculates a variance value of the main phase error detection value e main , i obtained out of the reception signal ri having a predetermined number of symbols . the variance value thus acquired is output to a comparator 63 as a control error value v main . the control error value v main is calculated based on the result of the multiplication performed by the multiplier 41 - 1 , i . e ., on the main phase error detection value e main , i representing the detected phase error remaining in the signal having undergone the phase control by the main pll circuit 31 - 1 . for that reason , the control error value v main denotes the error of the phase control carried out by the main pll circuit 31 - 1 . the sub pll control error detector 62 receives the sub pll intermediate signal fed from the sub pll circuit 31 - 2 every time the reception signal ri is input . for example , the sub pll control error detector 62 calculates a variance value of the sub phase error detection value e sub , i obtained out of the reception signal ri having a predetermined number of symbols . the variance value thus acquired is output to the comparator 63 as a control error value v sub . the control error value v sub is calculated based on the result of the multiplication performed by the multiplier 41 - 2 , i . e ., on the sub phase error detection value e sub , i representing the detected phase error remaining in the signal having undergone the phase control by the sub pll circuit 31 - 2 . for that reason , the control error value v sub denotes the error of the phase control carried out by the sub pll circuit 31 - 2 . the comparator 63 compares in magnitude the control error value v main supplied from the main pll control error detector 61 with the control error value v sub fed from the sub pll control error detector 62 . the result of the comparison is output to the loop gain control portion 34 in response to a comparison result output notification supplied from a timer 64 . as described , the loop filter 43 - 1 of the main pll circuit 31 - 1 and the loop filter 43 - 2 of the sub pll circuit 31 - 2 use the different loop gains g 1 main and g 1 sub . it follows that a difference reflecting the discrepancy between the loop gains g 1 main and g 1 sub appears in the control error value v main calculated by the main pll control error detector 61 and in the control error value v sub computed by the sub pll control error detector 62 . the foregoing paragraphs discussed an example in which the control error values v main and v sub are calculated based on the main and sub phase error detection values e main , i and e sub , i . alternatively , the control error values v main and v sub may be computed based on the signal d main , i ; on the filtering result θ main , i and signal d sub , i ; or on the filtering result θ sub , i . the timer 64 starts counting time upon receipt of an initialization flag fed from the loop gain control portion 34 . upon elapse of a predetermined count time , the timer 64 outputs a comparison complete notification to the loop gain control portion 34 . the time it takes to calculate the control error value is preset on the timer 64 , and the preset time is counted by the timer 64 . the timer 64 also outputs a comparison result output notification to the comparator 63 simultaneously with outputting the comparison complete notification to the loop gain control portion 34 . the loop gain control portion 34 has a gain control sequencer 72 furnished inside . the loop gain control portion 34 searches for optimum loop gains while monitoring the operation status of the main and sub pll circuits 31 - 1 and 31 - 2 , and establishes the detected optimum loop gains for their respective loop filters . for example , if the control error value v main calculated by the main pll control error detector 61 is larger than the control error value v sub computed by the sub pll control error detector 62 , the loop gain control portion 34 sets the same value as the loop gain g 1 sub to the loop filter 43 - 1 of the main pll circuit 31 - 1 , replacing the previously established loop gain g 1 main . that the control error value v main is larger than the control error value v sub signifies that synchronous acquisition can be performed with less error by establishing the loop gain g 1 sub set to the loop filter 43 - 2 of the sub pll circuit 31 - 2 . thus in this case , the loop gain g 1 main for the loop filter 43 - 1 of the main pll circuit 31 - 1 is replaced by the loop gain g 1 sub . if the control error value v sub calculated by the sub pll control error detector 62 is larger than the control error value v main computed by the main pll control error detector 61 , the gain control sequencer 72 of the loop gain control portion 34 leaves the loop gain g 1 main unchanged for the loop filter 43 - 1 of the main pll circuit 31 - 1 . that the control error value v sub is larger than the control error value v main as described above signifies that using the loop gain g 1 main unchanged allows synchronous acquisition to be performed with less error than if the loop gain g 1 sub is utilized . thus in this case , the loop gain g 1 main for the loop filter 43 - 1 of the main pll circuit 31 - 1 will not be replaced by the loop gain g 1 sub . as described , after it has been determined whether or not to replace the loop gain g 1 main , the loop gain g 1 sub for the loop filter 43 - 2 is changed . then another comparison is made in magnitude between the control error value v sub and the control error value v main so as to determine whether or not to replace the loop gain g 1 main . in this manner , searches continue for the optimum loop gains . when the loop gain g 1 sub is to be changed , the gain control sequencer 72 establishes the loop gain g 1 sub using the formula of g 1 sub = g 1 sub + α , where α stands for the smallest step of the established g 1 being quantized . in this case , if the established g 1 sub exceeds a maximum tolerable value g 1 max , the loop gain control portion 34 outputs a search complete signal . the loop gain control portion 34 causes an internally furnished transmission mode - specific gain selection portion 71 to hold the loop gain g 1 main for each of the transmission modes involved for selective loop gain output . for this reason , the transmission mode - specific gain selection portion 71 possesses as many registers as the maximum number n of the transmission modes involved ( e . g ., n = 8 ), each register being used to hold an optimum loop gain for the transmission mode in question . it is assumed that these registers give output values g 1 main0 , g 1 main1 , . . . g 1 mainn − 1 . the transmission mode of the reception signal ri , the modulation technique adopted for each transmission mode , and the modulation slots assigned to the transmission mode in question are identified by the tmcc fed from an error correction decoder 91 . a transmission mode number generator 92 counts the received symbols starting from an input frame start flag and , based on the received symbol count value , identifies which modulation slot the currently received symbol belongs to . also , based on information acquired from the tmcc signal and representing the modulation slots assigned to each transmission mode , the transmission mode number generator 92 determines the number tm identifying the transmission mode of the currently received symbol ( tm is called the transmission mode number ) and outputs the transmission mode number tm to the loop gain control portion 34 . for example , if the currently received transmission scheme has as many as “ n ” transmission modes multiplexed therein , then the transmission mode numbers tm are 0 , 1 , . . . n − 1 . the gain control sequencer 72 holds a transmission mode number tmtarget about which a search for an optimum loop gain is to be made . only during reception of the symbols for which tm = tmtarget , does the gain control sequencer 72 allow the pll control error comparator 33 and transmission mode - specific gain selection portion 71 to operate . the gain control sequencer 72 outputs an update en ( enable ) signal that goes high during reception of the symbols for which tm = tmtarget , to the pll control error comparison portion 33 and transmission mode - specific gain selection portion 71 . while the update en signal is being high , the pll control error comparison portion 33 carries out the processes discussed above . where the loop gain g 1 main is to be replaced by the loop gain g 1 sub while the update en signal is being high , an update flag generation portion inside the transmission mode - specific gain selection portion 71 outputs a flag for writing to a loop gain register corresponding to the transmission mode number tm currently in effect . when the frequency / phase synchronizing circuit shown in fig5 is started , the transmission mode number about which a search for the optimum loop gain is to be made is initialized ( tmtarget = 0 ). then the loop gains for the main and sub pll circuits 31 - 1 and 31 - 2 are initialized . after the loop gains for the main and sub pll circuits 31 - 1 and 31 - 2 have been initialized , the loop gain control portion 34 outputs an initialization flag to the pll control error comparison portion 33 . upon receipt of the initialization flag from the loop gain control portion 34 , the pll control error comparison portion 33 resets the currently effective result of the control error value comparison as well as the timer 64 . thereafter , the pll control error comparison portion 33 calculates the control error value v main , i and v sub , i as discussed above . the comparator 63 starts comparing these control error values in magnitude . upon being reset , the timer 64 of the pll control error comparison portion 33 starts counting time . when the count time necessary for calculating the control error value is reached , the timer 64 outputs a comparison complete notification to the loop gain control portion 34 . at the same time , the timer 64 outputs a comparison result output command to the comparator 63 . this in turn causes the comparator 63 to output the result of the control error comparison to the loop gain control portion 34 . given the control error comparison result , the loop gain control portion 34 controls accordingly the loop gains to be supplied to the loop filters 43 - 1 and 43 - 2 . at this point , if the loop gain g 1 main is to be replaced by the loop gain g 1 sub , the gain control sequencer 72 feeds the loop gain g 1 sub to the transmission mode - specific gain selection portion 71 as discussed above . the transmission mode - specific gain selection portion 71 updates the value held in a loop gain register g 1 main [ tm ], one of a plurality of internal registers which corresponds to the transmission mode number tm , by use of the value input from the gain control sequencer 72 . also , the transmission mode - specific gain selection portion 71 selects from g 1 main0 , g 1 main1 , . . . g 1 mainn − 1 the loop gain corresponding to the transmission mode number tm fed from the transmission mode number generator 92 , and outputs the selected loop gain as the loop gain for the loop filter 43 - 1 . if a search complete signal is output from the gain control sequencer 72 before a comparison complete notification is received from the pll control error comparison portion 33 , then a check is made to see if the tmtarget value equals n − 1 so as to determine whether the search for the optimum gains for all transmission modes has been completed . if the tmtarget value is not equal to n − 1 , then the tmtarget value is incremented by 1 in order to make a search for the optimum gain for the next transmission mode . at the same time , the loop gains for the main and sub pll circuits 31 - 1 and 31 - 2 are again initialized . in the manner described above , the search is made for the optimum loop gain regarding each of the tmtarget values 0 through n − 1 . this makes it possible to establish the optimum loop gain for each of the transmission modes involved based on different modulation techniques . alternatively , if a search complete signal is output from the gain control sequencer 72 before a comparison complete notification is received from the pll control error comparison portion 33 and if the tmtarget value is equal to n − 1 , then the tmtarget value may be reset to 0 . that is , after the search has been made for the optimum loop gain regarding each of the tmtarget values 0 through n − 1 , another search may again be started for an optimum loop gain regarding each of the tmtarget values 0 through n − 1 . in this manner , even where there exists time jitter in the transmission characteristics of the transmission channels involved , searches for optimum loop gains can be made continuously and the detected loop gains may be used uninterruptedly . explained below in reference to the flowchart of fig6 is a typical loop gain control process performed by the frequency / phase synchronizing circuit shown in fig5 . in step s 11 , the gain control sequencer 72 initializes the variable tmtarget to 0 . in step s 12 , the gain control sequencer 72 initializes that loop gain register inside the transmission mode - specific gain selection portion 71 which corresponds to the variable tmtarget . in this example , the setting of the loop gain register in question is represented by g 1 main — new and the initial value thereof by g 1 init . the setting g 1 main — new is used as the loop gain g 1 main for the loop filter 43 - 1 . also in step s 12 , the gain control sequencer 72 initializes the loop gain g 1 sub for the loop filter 43 - 2 . the initial value of the loop gain g 1 sub is the smallest loop gain that is g 1 min . the setting g 1 sub is used as the loop gain g 1 sub for the loop filter 43 - 2 . step s 13 is reached following the loop gain initialization . in step s 13 , the loop gain control portion 34 outputs an initialization flag to the pll control error comparison portion 33 . upon receipt of the initialization flag , the pll control error comparison portion 33 resets the result of the control error comparison carried out so far as well as the count value on the internal timer . also , the main pll control error detector 61 of the pll control error comparison portion 33 calculates the control error value v main based on the main pll intermediate signal output from the main pll circuit 31 - 1 . the sub pll control error detector 62 computes the control error value v sub based on the sub pll intermediate signal output from the sub pll circuit 31 - 2 . after being reset , the timer 64 starts counting time . upon elapse of a predetermined count time necessary for calculating the control error values v main and v sub , the timer 64 outputs a comparison complete notification to the loop gain control portion 34 . at the same time , the timer 64 outputs a comparison result output command to the comparator 63 . in response to the comparison result output command , the comparator 63 outputs the result of the comparison in magnitude between the control error values v main and v sub to the loop gain control portion 34 . in step s 14 , the gain control sequencer 72 determines whether the comparison complete notification output from the timer 64 is detected . if it is determined that the comparison complete notification is not detected yet , control is passed on to step s 20 . in step s 20 , it is determined whether a search complete signal is output . if it is determined that the search complete signal is not output yet , control is passed on to step s 21 . in step s 21 , the comparison complete notification from the timer 64 is polled at intervals of a predetermined time period in a wait state . thereafter , control is returned to step s 14 . if it is determined in step s 14 that the comparison complete notification is detected , control is passed on to step s 15 . in step s 15 , the gain control sequencer 72 determines whether v main & gt ; v sub based on the comparison result fed from the comparator 63 . if it is determined in step s 15 that v main & gt ; v sub then step s 16 is reached . in step s 16 , the gain control sequencer 72 replaces the loop gain g 1 main — new with g 1 sub currently established as the loop gain for the loop filter 43 - 2 . at this point , the gain control sequencer 72 outputs a predetermined signal to the update flag generation portion inside the transmission mode - specific gain selection portion 71 . in turn , the update flag generation portion outputs a flag for writing to the loop gain register corresponding to the transmission mode number tm currently in effect . if it is determined in step s 15 that v main ≦ v sub instead of v main & gt ; v sub , then step s 16 is skipped . in step s 17 , the gain control sequencer 72 establishes g 1 sub + α and updates the loop gain g 1 sub therewith , where a denotes the amount of gain corresponding to the smallest step of the loop gain g 1 ( g 1 main or g 1 sub ) being quantized . in step s 18 , the gain control sequencer 72 determines whether the loop gain g 1 sub updated in step s 17 exceeds the maximum tolerable value g 1 max . if it is determined in step s 18 that the loop gain g 1 sub has exceeded the maximum value g 1 max , control is passed on to step s 19 . in step s 19 , the gain control sequencer 72 outputs a search complete signal . if it is determined in step s 18 that the loop gain g 1 sub has not exceeded the maximum value g 1 max , then step s 19 is skipped . control is returned to step s 13 if it is determined in step s 18 that the loop gain g 1 sub has not exceeded the maximum value g 1 max , or after step s 19 has been completed . after the search complete signal is output in step s 19 , the signal output is confirmed in step s 20 . thereafter , control is returned to step s 22 . in step s 22 , the gain control sequencer 72 determines whether the variable tmtarget is equal to n − 1 . if it is determined that the variable tmtarget is not equal to n − 1 , control is passed on to step s 23 . in step s 23 , the gain control sequencer 72 increments the variable tmtarget by 1 . control is then returned to step s 12 . that is , another search is made here for the optimum loop gain for the next transmission mode number . if it is determined in step s 22 that the variable tmtarget is equal to n − 1 , control is returned to step s 11 . that is , after the search has been made for the optimum loop gains for all transmission mode numbers , a second search is started for the optimum loop gain for each of the tmtarget values 0 through n − 1 . in the second and subsequent searches , there is no need to initialize g 1 main — new in step s 12 . alternatively , if it is determined in step s 22 that the variable tmtarget is equal to n − 1 , the loop gain control process may be terminated . the loop gain control process is carried out in the manner described above . thus according to the present disclosure , it is possible to search for optimum loop gains in keeping with the individual differences between receivers and the time jitter over transmission channels even where a plurality of modulation techniques are used in the transmission frame . the foregoing paragraphs have explained examples in which the search is made for the optimum loop gain as the loop gain g 1 for use in direct multiplications performed on the detected phase error in the frequency / phase synchronizing circuit . alternatively , a search may be made for the loop gain g 2 for use in the multiplication to be performed on the phase error resulting from the multiplication using the loop gain g 1 . as another alternative , searches may be made for both the loop gain g 1 and the loop gain g 2 . fig7 is block diagram showing a typical configuration of a first embodiment of a receiving system to which the frequency / phase synchronizing circuit of the embodiments of the present disclosure is applied . the receiving system of fig7 is made up of an acquisition portion 101 , a transmission channel decoding process portion 102 , and an information source decoding process portion 103 . the acquisition portion 101 acquires a signal via transmission channels such as terrestrial digital broadcasts , satellite digital broadcasts , catv networks and the internet , not shown , and forwards the acquired signal to the transmission channel decoding process portion 102 . given the signal acquired by the acquisition portion 101 via the transmission channels , the transmission channel decoding process portion 102 performs a transmission channel decoding process including synchronized detection and error correction on the received signal , and forwards the signal resulting from the decoding process to the information source decoding process portion 103 . that is , the transmission channel decoding process 102 includes the structure of the frequency / phase synchronizing circuit shown in fig5 that performs the above - mentioned synchronized detection . the information source decoding process portion 103 performs an information source decoding process on the signal having undergone the transmission channel decoding process , the information source decoding process including the process of expanding the compressed information back to the original information whereby the transmitted data is acquired . that is , the signal acquired by the acquisition portion 101 via the transmission channels may have undergone compression coding whereby the original information was compressed so as to reduce the amount of the data such as video and audio data . in such a case , the information source decoding process portion 103 performs the information source decoding process on the signal having undergone the transmission channel decoding process , the information source decoding process including the process of expanding the compressed information back to the original information . if the signal acquired by the acquisition portion 101 via the transmission channels has not undergone compression coding , the information source decoding process portion 103 does not perform the process of expanding the compressed information back to the original information . the expanding process includes mpeg decoding , for example . the information source decoding process may include descrambling in addition to the expanding process . the receiving system of fig7 may be applied to tv tuners for receiving digital tv broadcasts , for example . the acquisition portion 101 , transmission channel decoding processing portion 102 , and information source decoding processing portion 103 may each be implemented in the form of an independent device ( hardware ( e . g ., ic ( integrated circuit )) or a software module ). alternatively , the acquisition portion 101 , transmission channel decoding processing portion 102 , and information source decoding processing portion 103 may be implemented altogether as an independent device . as another alternative , the acquisition portion 101 and transmission channel decoding processing portion 102 may be implemented in combination as an independent device . as a further alternative , the transmission channel decoding processing portion 102 and information source decoding processing portion 103 may be implemented in combination as an independent device . fig8 is block diagram showing a typical configuration of a second embodiment of the receiving system to which the frequency / phase synchronizing circuit of the embodiments of the present disclosure is applied . of the components in fig8 , those with their corresponding counterparts shown in fig7 are designated by like reference numerals , and their explanations may be omitted where appropriate . the configuration of the receiving system in fig8 is common to the configuration of its counterpart in fig7 in that the acquisition portion 101 , transmission channel decoding process portion 102 , and information source decoding process portion 103 are provided . on the other hand , the configuration of fig8 is different from that of fig7 in that an output portion 111 is additionally provided . the output portion 111 may be typically composed of a display device for displaying images and of speakers for outputting sounds . as such , the output portion 111 outputs images and sounds derived from the signal output from the information source decoding process portion 103 . in short , the output portion 111 is a component that outputs images and / or sounds . the receiving system of fig8 may be applied to tv sets for receiving digital tv broadcasts and to radio receivers for receiving radio broadcasts , for example . if the signal acquired by the acquisition portion 101 has not undergone compression coding , then the signal output from the transmission channel decoding process portion 102 is fed directly to the output portion 111 . fig9 is block diagram showing a typical configuration of a third embodiment of the receiving system to which the frequency / phase synchronizing circuit of the embodiments of the present disclosure is applied . of the components in fig9 , those with their corresponding counterparts shown in fig7 are designated by like reference numerals , and their explanations may be omitted where appropriate . the configuration of the receiving system in fig9 is common to the configuration of its counterpart in fig7 in that the acquisition portion 101 and transmission channel decoding process portion 102 are provided . on the other hand , the configuration of fig9 is different from that of fig7 in that the information source decoding process portion 103 is not provided and a recording portion 121 is additionally furnished . the recording portion 121 records ( stores ) the signal ( e . g ., ts packets in the mpeg format ) output from the transmission channel decoding process portion 102 to recording ( storage ) media such as optical disks , hard disks ( magnetic disks ), and flash memories . the above - described receiving system of fig9 may be applied to recorders for recording tv broadcasts , for example . as another example , the receiving system of fig9 may be furnished with the information source decoding process portion 103 . in this case , the recording portion 121 may record the signal having undergone the information source decoding process performed by the information source decoding process portion 103 , i . e ., images and sounds acquired through the decoding process . the series of processes described above may be executed either by hardware or by software . where the software - based processing is to be carried out , the programs constituting the software may be either incorporated beforehand in the dedicated hardware of the computer to be used , or installed upon use over a network or from a suitable recording medium into a general - purpose personal computer or like equipment such as a personal computer 700 shown in fig1 capable of executing diverse functions based on the installed programs . in fig1 , a cpu ( central processing unit ) 701 performs various processes in accordance with the programs stored in a rom ( read only memory ) 702 or according to the programs loaded from a storage device 708 into a ram ( random access memory ) 703 . the ram 703 may also accommodate data and other resources needed by the cpu 701 in carrying out diverse processing . the cpu 701 , rom 702 , and ram 703 are interconnected via a bus 704 . an input / output interface 705 is also connected to the bus 704 . the input / output interface 705 is connected with an input device 706 , output device 707 , storage device 708 , and communication device 709 . the input device 706 is generally composed of a keyboard and a mouse . the output device 70 is usually constituted by a display unit such as lcd ( liquid crystal display ) and speakers . the storage device 708 is typically formed by a hard disk . the communication device 709 is ordinarily structured with a modem and a network interface such as a lan card . the communication device 709 conducts communications over networks including the internet . a drive 710 may be further connected as needed to the input / output interface 705 . a piece of removable media 711 such as magnetic disks , optical disks , magneto - optical disks or semiconductor memories may be loaded into the drive 710 . computer programs may be retrieved from the loaded removable medium and installed as needed into the storage device 708 . where the above - described series of processes is to be executed by software , the programs making up the software may be installed over networks including the internet or from recording media such as the removable media 711 . as shown in fig1 , the recording media which are offered to users apart from their computers and which accommodate the programs may be constituted not only by the removable media 711 such as magnetic disks ( including floppy disks ( registered trademark )), optical disks ( including cd - rom ( compact disk read - only memory ) and dvd ( digital versatile disk )), magneto - optical disks ( including md ( mini - disk ; registered trademark )), or semiconductor memories ; but also by such recording media as the rom 702 or hard disks contained in the storage device 708 . the latter recording media with the programs stored thereon are preinstalled in the computer when offered to the user . in this specification , the series of the processes discussed above include not only the processes carried out in the depicted sequence ( i . e ., on a time series basis ) but also processes that may be conducted parallelly or individually and not necessarily chronologically . it should be understood by those skilled in the art that various modifications , combinations , sub - combinations and alterations may occur depending on design requirements and other factors in so far as they are within the scope of the appended claims or the equivalents thereof . the present disclosure contains subject matter related to that disclosed in japanese priority patent application jp 2010 - 219644 filed in the japan patent office on sep . 29 , 2010 , the entire content of which is hereby incorporated by reference .