please refer to fig4 , which is a circuit diagram of a gyrator 10 having a gyrator core gci of the preferred embodiment according to the present invention . in addition to the gyrator core gci , the gyrator 10 further comprises an input common mode feedback section 12 , and an output common mode feedback section 14 different from the common mode feedback section cmii of the gyrator ncg shown in fig1 , which comprises two non - reverse series connection inverter sets , the input common mode feedback section 12 comprises two reverse series connection inverter sets , a forward - reverse series connection inverter set 16 and a backward - reverse series connection inverter set 18 , each of which comprises an inverter cmi 1 , an inverter cmi 2 , and an input feedback resister r fi1 electrically connected in parallel with the inverter cmi 2 . similarly , the output common mode feedback section 14 comprises two reverse series connection inverter sets , each of which comprises an inverter cmo 1 , an inverter cmo 2 , and an output feedback resister r f01 electrically connected in parallel with the inverter cmo 2 . according to the preferred embodiment , any one of the inverters of the gyrator 10 can comprise a transistor , and the transistor can be a mos , a coms , or a bi - polar transistor . the gyrator 10 has a larger dc gain a 0 due to the installation of the feedback resistor r fi1 ( r fo1 ), and this is described as follows . please refer to fig5 , which is an equivalent circuit diagram of the forward - reverse connection inverter set 16 ( the backward - reverse connection inverter set 18 is similar ) of the input common mode feedback section 12 ( the output common mode feedback section 14 is similar ) of the gyrator 10 shown in fig4 . in fig5 , current flowing into an intermediate point v x is equal to current flowing out from the intermediate point v x , that is yf1 ( vi1 − vx )+ yf2 ( vi2 − vx )= ym1vi1 + ym2vi2 +( yo1 + y02 ) vx ( eq . 5 ). eq . 5 can be derived as - v x = ( y m ⁢ ⁢ 1 - y f ⁢ ⁢ 1 y x ) ⁢ ⁢ v i ⁢ ⁢ 1 + ( y m ⁢ ⁢ 2 - y f ⁢ ⁢ 2 y x ) ⁢ ⁢ v i ⁢ ⁢ 2 , ( eq . ⁢ 6 ) where yx = yo1 + yo2 + yf1 + yf2 . based on eq . 6 , a relation between i i1 , i i2 , v i1 , and v i2 can be derived as : i i ⁢ ⁢ 1 = y i ⁢ ⁢ 1 ⁢ v i ⁢ ⁢ 1 + y f ⁢ ⁢ 1 ⁡ ( v i ⁢ ⁢ 1 - v x ) = ( y i ⁢ ⁢ 1 + y f ⁢ ⁢ 1 + y f ⁢ ⁢ 1 ⁢ y m ⁢ ⁢ 1 - y f ⁢ ⁢ 1 y x ) ⁢ ⁢ v i ⁢ ⁢ 1 + y f ⁢ ⁢ 1 ⁢ y m ⁢ ⁢ 2 - y f ⁢ ⁢ 2 y x ⁢ v i ⁢ ⁢ 2 ⁢ ⁢ and ( eq . ⁢ 7 ) i i ⁢ ⁢ 2 = y i ⁢ ⁢ 2 ⁢ v i ⁢ ⁢ 2 + y f ⁢ ⁢ 2 ⁡ ( v i ⁢ ⁢ 2 - v x ) = y f ⁢ ⁢ 2 ⁢ y m ⁢ ⁢ 1 - y f ⁢ ⁢ 1 y x ⁢ v i ⁢ ⁢ 1 + ( y i ⁢ ⁢ 2 + y f ⁢ ⁢ 2 + y f ⁢ ⁢ 2 ⁢ y m ⁢ ⁢ 2 - y f ⁢ ⁢ 2 y x ) ⁢ ⁢ v i ⁢ ⁢ 2 . ( eq . ⁢ 8 ) [ i i ⁢ ⁢ 1 i i ⁢ ⁢ 2 ] = ⁢ [ y i ⁢ ⁢ 1 + y f ⁢ ⁢ 1 + y f ⁢ ⁢ 1 ⁢ y m ⁢ ⁢ 1 - y f ⁢ ⁢ 1 y x y f ⁢ ⁢ 1 ⁢ y m ⁢ ⁢ 2 - y f ⁢ ⁢ 2 y x y f ⁢ ⁢ 2 ⁢ y m ⁢ ⁢ 1 - y f ⁢ ⁢ 1 y x y i ⁢ ⁢ 2 + y f ⁢ ⁢ 2 + y f ⁢ ⁢ 2 ⁢ y m ⁢ ⁢ 2 - y f ⁢ ⁢ 2 y x ] ⁢ [ v i ⁢ ⁢ 1 v i ⁢ ⁢ 2 ] = ⁢ [ y 11 y 12 y 21 y 22 ] ⁡ [ v i ⁢ ⁢ 1 v i ⁢ ⁢ 2 ] ( eq . ⁢ 9 ) without losing the generality , all of the inverters of the gyrator 10 are assumed to be identical and have a feedback resistance of r f = 1 / g f , that is y i1 = y i2 = y i , y o1 = y o2 = y o , y f1 = y f , y f2 = y f + g f , and y m1 = y m2 = y m . therefore , an admittance matrix of the input common mode feedback section 12 can be derived as y cm = [ y 11 + y 22 0 y 12 + y 21 0 0 y 11 + y 22 0 y 12 + y 21 y 12 + y 21 0 y 11 + y 22 0 0 y 12 + y 21 0 y 11 + y 22 ] . similarly , assume differential signal is applied to the gyrator 10 . therefore , the admittance matrix can be simplified as y gyr = [ y l - y m y m y l ] , ⁢ where ⁢ ⁢ y l = ( y 11 + y 22 ) - ( y 12 + y 21 ) + ( y i + 2 ⁢ y f + y o ) , and ⁢ ⁢ y l = 3 ⁢ y i + 4 ⁢ y f + y 0 + g f ⁡ ( 2 ⁢ y o + 2 ⁢ y f ) 2 ⁢ y o + 2 ⁢ y f + g f ( eq . ⁢ 10 ) in accordance with eq . 10 , an equivalent circuit diagram of y l is shown in fig6 . it is apparent that the installation of the feedback resistor r fi1 ( r fo1 ) increases the impedance of y l , and the gyrator 10 has therefore a higher dc gain a 0 . the stable condition of gyrator 10 is derived as follows . under an assumption that differential signal is applied to the gyrator 10 , the admittance matrix ygyr of the gyrator 10 can be represented as y gyr = [ y li - y mo y mi y lo ] , where y li is an input loading admittance , y lo is an output loading admittance , y mi is a trans - admittance from an input end to an output end , and y mo is another trans - admittance from the output end to the input end . the channel delay effect is taken into consideration , that is y mi y mo = g m 2 e − 2sτ , where τis an effective channel delay of the gyrator core gci , and g m is an effective gyrating constant . accordingly , the characteristic function of gyrator 10 can be derived as δ ⁡ ( s ) = 1 + y mi ⁢ y mo y li ⁢ y lo = 1 + g m 2 ⁢ ⅇ - 2 ⁢ s ⁢ ⁢ τ y le 2 ⁡ ( s ) = 1 + f d ⁡ ( s ) = 1 + f ⁡ ( s ) ⁢ ⅇ - 2 ⁢ s ⁢ ⁢ τ , ( eq . ⁢ 11 ) where y le 2 ( s ) is an effective loading product of the gyrator core gci , f d ( s ) is a loop transfer function , and f ( s ) is another loop transfer function without taking the channel delay effect into consideration . the stable condition of the gyrator 10 is sustained if all of zeros of δ ( s ) are located in the left half region of the s - plane . whether or not a zero of δ ( s ) is located in the left half region of the s - plane can be determined through an application of a nyquist plot . it can be seen from eq . 10 that y l is a network comprising nothing but resistors and capacitors , so y l can be further simplified as yi ⁡ ( s ) = g 1 + sc 1 + g f ⁡ ( g 2 + sc 2 ) g f + ( g 2 + sc 2 ) , ( eq . ⁢ 12 ) where g 1 = g o , g 2 = 2g o , c 2 = 2c f + 2c o , and c 1 = 3c i + 4c f + c o + c ext , where c ext is an external capacitance of the gyrator 10 . please refer to fig7 , which is an equivalent circuit diagram of the simplified y l . eq . 12 can be rewritten as yi ⁡ ( s ) = ( g f + g 1 + sc 1 ) - g f 2 g f + g 2 + sc 2 = c 1 ⁡ ( s + z 1 ) ⁢ ( s + z 2 ) ( s + p 2 ) , ( eq . ⁢ 13 ) where − p 2 =−( gf + g2 )/ c2 & lt ; 0 is a pole of yl ( s ), and − z 1 and − z 2 are two zeros . a curve yl ( s ) shown in fig8 is obtained if s in eq . 13 changes along a negative real axis ( s = 0 →−∞), wherein when s = 0 , yl ( s )& gt ; 0 , when s =− p 2 + , yl ( s )→−∞, when s =− p 2 − , yl ( s )→∞, and when s →−∞, yl ( s )→−∞. because yl ( s ) is a continuous function besides the pole − p 2 , the two zeros − z 1 and − z 2 are easily determined to be two negative real numbers with the pole − p 2 located between the two zeros − z 1 and − z 2 . without losing the generality , the pole − p 2 and the two zeros − z 1 and − z 2 are assumed to be located in an order of z 2 & gt ; p 2 & gt ; z 1 . 1 . neither f d ( s ) nor f ( s ) has any pole or zero located in the right half region of the s - plane ; hence , whether or not the gyrator is stable now can be determined through observing whether the nyquist plot of f d ( s ) when s = j ∞→ j0 encircles a specific point (− 1 , j0 ). when s changes along a positive imaginary axis ( s = j0 → j ∞), each of |( s + z1 )/( s + p2 )| and |( s + z2 )| is a monotonic increasing function , so when w = 0 −∞, | y l ( jw )| is also a monotonic increasing function , while | f d ( jw )|=| f ( jw )| is a monotonic decreasing function . moreover , a deduction of ∠ yl ( s )=∠( s + z 1 )+∠( s + z 2 )−∠( s + p 2 ) can obtain ∠ y l ( jw )≧∠( jw + z2 )≧ 0 and ∠ y l ( jw )& lt ;∠( jw + z 1 )& lt ; π / 2 , so − π & lt ;∠ f ( jw )≧ 0 . since a phase delay − 2wτ due to the channel delay effect is also a monotonic decreasing function , ∠ f d ( jw )≧ 0 . in summary , the stable condition of the gyrator 10 can be represented through the introduction of a concept of gain margin , that is | f d ( jw 0 )|& lt ; 1 , where w 0 is an existing smallest positive real number making ∠ f d ( jw 0 )=− π or | y le 2 ( jw 0 )|& gt ; g m 2 , where w 0 is a smallest positive real number making 2w 0 τ +∠ y le 20 ( jw 0 )= π . however , the solution to this is not easy to obtain . since | f d ( jw )| is a monotonic decreasing function when w = 0 →∞, if a positive real number w 0 makes | f d ( jw 0 )|= 1 and ∠ f d ( jw ) is restricted to be within a specific function larger than − π when w ≧ w 0 , the system is stable . in short , through the introduction of a bounding function and the concept of a phase margin , a sufficient condition for stability can be obtained . for example , assume y p ( s ) has the following characteristics : when w = 0 →∞, if ∠ y p ( jw ) is a monotonic increasing function and ∠ y p ( jw )≧∠ y l ( jw ), y p ( s ) is a phase upper bound function of y l ( s ). based on the above , if a positive real number w 0 makes | f d ( jw 0 )|= 1 and 2w 0 τ +∠ y pi ( jw 0 )+∠ y po ( jw 0 )≧ π , where y pi ( s ) and y po ( s ) are two phase upper bound functions of y li ( s ) and y lo ( s ) respectively , 0 ≧∠ f d ( jw )& gt ;− π when w ≧ w 0 , and the system is determined to be stable . similarly , assume y a ( s ) has the following characteristics : when w = 0 →∞, if | y a ( jw )| is a monotonic increasing function and | y a ( jw )|≧| y l ( jw )|, y a ( s ) is an amplitude lower bound function of y l ( s ). based on the above , if a positive real number w 0 makes | y ai ( jw 0 )|*| y ao ( jw 0 )|= g m 2 and 2w 0 τ +∠ y pi ( jw 0 )+∠ y po ( jw 0 )& lt ; π , where y ai ( s ) and y ao ( s ) are two amplitude lower bound functions of y li ( s ) and y lo ( s ) respectively , when w & gt ; w 0 | f d ( jw )|& lt ; 1 and when w ≧ w 0 0 ≧∠ f d ( jw )& gt ;− π , and the system is determined to be stable . yi ⁡ ( jw ) = g 1 + j ⁢ ⁢ ω ⁢ ⁢ c 1 + g f ⁡ ( g 2 + j ⁢ ⁢ ω ⁢ ⁢ c 2 ) g f + ( g 2 + j ⁢ ⁢ ω ⁢ ⁢ c 2 ) = g 1 + g 3 + g f 2 g f + g 2 * k 1 + k + j ⁢ ⁢ ω ⁢ [ c 1 + c 3 ⁡ ( 1 - k 1 + k ) ] ( eq . ⁢ 14 ) is obtained , where k =( wc 2 ) 2 /( g f + g 2 ) 2 & gt ; 0 , g 3 =( g f g 2 )/( g f + g 2 ), and c 3 = c 2 ( g f /( g f + g 2 )) 2 . it can be seen from eq . 14 that y pi ( s )=( g 1 + g 3 )+ s ( c 1 + c 3 ) is a phase upper bound function of y l ( s ). naturally , y p2 ( s )=( g 1 + g 3 )+ s ( c 1 + c 2 ) is also a phase upper bound function of y l ( s ). on the other hand , y a1 ( s )=( g 1 + g 3 )+ sc 1 is an amplitude lower bound function of y l ( s ). naturally , y a2 ( s )= g 1 + sc 1 and y a3 ( s )= sc 1 are another amplitude lower bound functions of y l ( s ). through the use of the above bounding functions , a stable condition can be obtained . for example , when all of the inverters of the gyrator 10 are identical and all the feedback resistors are also identical , the above y a3 ( s ) and y pi ( s ) are selected to be the bounding functions of y l ( s ), and one sufficient condition for the stability of the gyrator 10 is w 0 = gm / c1 and w 0 τ +∠ y pi ( jw 0 )& lt ; π / 2 , or tan ( w 0 τ )& lt ;( g 1 + g 3 )/( w 0 ( c 1 + c 3 ))= c 1 ( g 1 + g 3 )/( g m ( c 1 + c 3 )), or tan ( c m / c 1 )& lt ; c 1 /( a 0 ( c 1 + c 3 )). in particular , when r f = 0 , y l ( s ) can be simplified as y l ( s )=( g 1 + g 2 )+ s ( c 1 + c 2 )= g + sc . since both | y l ( s )| and ∠ y l ( s ) are themselves monotonic increasing functions when w = 0 →∞, without any additional auxiliary of a bounding function , they can make use of the gain margin ( and the phase margin as well ) of f d ( s ) to be the stable condition of the gyrator 10 directly . for example , when all of the inverters of the gyrator 10 are identical , the necessary and sufficient condition for the stability of the gyrator 10 is w 0 = 1 c ⁢ ( g m 2 - g 2 ) = g m c ⁢ ( 1 - 1 a 0 2 ) and ⁢ ⁢ w 0 ⁢ τ + ∠ y l ⁡ ( j ⁢ ⁢ w 0 ) & lt ; π / 2 ⁢ ⁢ or ⁢ ⁢ tan ⁢ ⁢ ( w 0 ⁢ τ ) & lt ; g ω 0 ⁢ c = 1 ( a 0 2 - 1 ) ⁢ ⁢ or ⁢ ⁢ tan ⁢ ⁢ ( c m c ⁢ 1 - 1 a 0 2 & lt ; 1 ( a 0 2 - 1 ) ) . ( a 0 2 - 1 ) ⁢ tan ⁢ ⁢ ( c m c ⁢ 1 - 1 a 0 2 ) & lt ; ⁢ a 0 ⁢ c m c = g m ⁢ c m gc . therefore , g m c m & lt ; gc is a sufficient condition for the stability of the gyrator 10 . in contrast to the prior art , the present invention can provide a gyrator comprising a gyrator core and at least a common mode feedback section . the common mode feedback section comprises two reverse series connection inverter sets , each of which comprises an inverter cmi 1 , an inverter cmi 2 , and a feedback resistor electrically connected in parallel with the inverter cmi 2 . therefore , a dc gain of the gyrator is increased due to the installation of the feedback resistor . moreover , when the feedback resistor has a resistance equal to zero , the gyrator has a stable condition equal to tan ⁡ ( c m c ⁢ 1 - 1 a 0 2 ) & lt ; 1 ( a 0 2 - 1 ) . ( eq . ⁢ 15 ) in contrast to eq . 15 , the stable condition g * c is not smaller than gm * cm of the gyrator of the prior art is only a specific sufficient condition . those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention . accordingly , the above disclosure should be construed as limited only by the metes and bounds of the appended claims .