during testing or use of oximeters , a need exists for an improved method to switch between photodetectors and / or different signal processing paths of a photodetector . heretofore known switching between photo detectors and / or different signal processing paths of a photodetector has introduced undesirable signal transients that may set off oximeter monitor alarms and / or require longer periods of time for the transient to settle out of the normal five to twenty seconds averaging performed by a microprocessor of an oximeter monitor . accordingly , there is a need for improved methods , materials , and / or equipment to switch between photo detectors and / or different signal processing paths of a photo detector , e . g ., unfiltered and filtered channels of a pulse oximetry sensor . referring now to the drawings , the details of specific example embodiments are schematically illustrated . like elements in the drawings are represented by like numbers , and similar elements are represented by like numbers with a different lower case letter suffix . referring to fig1 , depicted is a schematic block diagram of a switchover , two channel , gain controlled oximeter sensor amplifier having a current output , according to a specific example embodiment of the present disclosure . a channel 1 input signal 102 may be applied to a gain controlled amplifier 114 , and a channel 2 input signal 108 may be applied to a gain controlled amplifier 116 . gains of the gain controlled amplifiers 114 and 116 may be controlled by gain control signal lines 106 and 112 , respectively . the outputs 118 and 120 of the gain controlled amplifiers 114 and 116 , respectively , are coupled to voltage - to - current converters 122 and 124 , respectively . the current outputs of voltage - to - current converters 122 and 124 may be connected in parallel so as to generate a single switchover output current signal 126 . voltage - to - current converters 122 and 124 may be , for example , but not limited to , optical isolators each having a voltage controlled light emitting diode as an input and a photodetector as an output . for example , at the beginning of a time period t , gain control signal line 106 has a control voltage 104 at a maximum v 1 thereby setting the gain of gain controlled amplifier 114 to a maximum . as the time period t proceeds , control voltage 104 decreases until it is at a minimum v 1 , thereby reducing the gain of gain controlled amplifier 114 . in a similar , but opposite fashion , gain control signal line 112 has a control voltage 110 that starts at the beginning of the time period t at a minimum v 2 which may set the gain of gain controlled amplifier 116 to a minimum , and as the time period t proceeds , control voltage 110 increases until it is at a maximum v 2 , thereby , according to an embodiment , increasing the gain of gain controlled amplifier 116 . output current 126 , according to an embodiment , represents the dominate gain controlled amplifier output signal 118 or 120 , e . g ., the one having the highest gain and signal input will block the other one . thus , input signal transfer may switch from one of the input channels to the other without introducing a transient in the output current signal 126 . referring to fig2 , depicted is a detailed schematic block diagram of a switchover , two channel , gain controlled oximeter sensor amplifier having a current output , according to another specific example embodiment of the present disclosure . a pulse oximetry peripheral probe 202 may comprise two light emitting diodes ( leds ), one in the visible red spectrum ( e . g ., 660 nm ), and the other in the infrared spectrum ( e . g ., 940 nm ). the sources of light from the two leds 230 pass through patient tissues to photodetector 232 . light wavelengths not absorbed by the tissues and blood supply are detected by photodetector 232 . a current - to - voltage converter 204 receives the current source signal from detector 232 and produces a voltage on signal line 102 that represents the amplitudes of the detected light wavelengths . a signal line 102 is coupled to an input of the gain controlled amplifier 114 and an input of an analog - to - digital converter 226 . the output of analog - to - digital converter 226 may be coupled to a digital filter 224 that may be used to enhance the signal information from the photo - detector 232 . a digital - to - analog converter 222 may be coupled to the output of a digital filter 224 so as to convert this output to an analog voltage that may be coupled to an input of gain controlled amplifier 116 . according to this specific example embodiment , the photodetector 232 may have an output that may be coupled directly ( or indirectly ) to the input of the gain controlled amplifier 114 . in addition , the output of the photodetector 232 may be coupled ( e . g ., indirectly ) to the gain controlled amplifier 116 through the digital filter 224 . this particular embodiment is directed , in one aspect , to providing a switchover between signal line 102 having the unprocessed information from the photodetector 232 and the signal line 108 having the digitally filtered ( enhanced ) information from the photodetector 232 . the controller 216 , e . g ., a digital processor , a microprocessor , a microcontroller , a digital signal processor ( dsp ), an application specific integrated circuit ( asic ) and / or programmable logic array ( pla ), in combination with digital - to - analog converters 218 and 220 may be used for controlling gains of the gain controlled amplifiers 114 and 116 . when a selection change , e . g ., nurse or doctor initiated , is made between the unfiltered and filtered signal information from the photodetector 232 , the gain control signal line 106 may have a control signal from the digital - to - analog converter 220 that is at a maximum voltage at the beginning of a time period t , thereby , according to this embodiment , setting the gain of the gain controlled amplifier 114 to a maximum . as the time period t proceeds , the control signal on the gain control signal line 106 decreases until it is at a minimum , thereby , according to this embodiment , reducing the gain of gain controlled amplifier 114 . in a similar , but opposite fashion , the gain control signal line 112 may have a control signal that starts at the beginning of the time period t at a minimum voltage thereby , according to this embodiment , setting the gain of the gain controlled amplifier 116 to a minimum , and as the time period t proceeds , the control signal on the gain control signal line 112 increases until it is at a maximum voltage , thereby , according to this embodiment , increasing the gain of the gain controlled amplifier 116 . since the outputs of the voltage - to - current converters 122 and 124 may be in parallel , the output current 126 may represent the dominant gain controlled amplifier output signal 118 or 120 , e . g ., the one having the highest gain and signal input will block the other one . thus , according to this embodiment , input signals 102 and 108 may be switched without introducing a transient in the output current signal 126 . the output current signal 126 may be used to supply sensor information to an oximeter 212 , e . g ., oximeter display monitor . the timing and clocking circuit 228 may be used for clock signals and timing signals for the light emitting diodes 230 and the controller 216 . while embodiments of this disclosure have been depicted , described , and are defined by reference to example embodiments of the disclosure , such references do not imply a limitation on the disclosure , and no such limitation is to be inferred . the subject matter disclosed is capable of considerable modification , alteration , and equivalents in form and function , as will occur to those ordinarily skilled in the pertinent art and having the benefit of this disclosure . the depicted and described embodiments of this disclosure are examples only , and are not exhaustive of the scope of the disclosure .
switchover of a filtered and unfiltered pulse oximetry sensor is provided with gain controlled amplifiers controlled by separate gain control voltages that may change in opposite directions over a period of time . the outputs of the gain controlled amplifiers may be coupled to voltage - to - current converters whose outputs may be coupled in parallel . the parallel coupled outputs of the voltage - to - current converters may produce a current signal representative of the output of the gain controlled amplifier having the highest gain / signal .