Input bias and signal conditioning circuit for differential amplifiers

Claim 2

An input bias circuit of interconnected unidirectional conductive devices for biasing an amplifier of the type having a pair of differential input signal terminals, comprising: first, second, third and fourth strings of series connected like poled unidirectional conductive devices, each string having at least one device therein, said first and fourth strings being connected in parallel and poled in opposite directions and said second and third strings being connected in parallel and poled in opposite directions, thereby forming two sets of parallel strings, said two sets being connected in series between the pair of differential input signal terminals of the amplifier, the junction between said two sets of parallel strings having a voltage potential applied thereto for normally providing bias current through said first and third strings to the pair of differential input signal terminals and for normally rendering said second and fourth strings non-conductive, said second and fourth strings becoming conductive to clamp the pair of differential input terminals to said junction potential when the magnitude of an input signal renders said first and third strings non-conductive.

Claim 3

The circuit of unidirectional conductive devices described in claim 1 wherein said unidirectional conductive devices are diodes.

Claim 4

The circuit of unidirectional conductive devices described in claim 2 wherein said first and third strings each include two diodes.

Claim 5

The circuit of unidirectional conductive devices described in claim 3 wherein said second and fourth strings each include one diode.

Claim 6

A diode circuit connected between first and second input terminals of a differential amplifier for providing bias and overload protection, comprising: a first diode having the cathode thereof connected to the first input terminal of the differential amplifier; a second diode having the cathode thereof connected to the anode of said first diode; a third diode having the cathode thereof connected to the anode of said second diode, the anode of said third diode being connected to the second input terminal of the differential amplifier; a fourth diode having the cathode thereof connected to the second input terminal of the differential amplifier; a fifth diOde having the cathode thereof connected to the anode of said fourth diode; a sixth diode having the cathode thereof connected to the anode of said fifth diode, the anode of said sixth diode being connected to the first input terminal of the differential amplifier; conductive means for connecting the junction of said first and second diodes with the junction of said fourth and fifth diodes, said conductive means having a voltage potential applied thereto to normally provide bias current through said second and third diodes to the second input terminal of the differential amplifier and bias current through said fifth and sixth diodes to the first input terminal of the differential amplifier, said first and fourth diodes being normally reversed biased and becoming conductive only when the magnitude of a signal current which may be applied to the amplifier input terminals exceeds the respective bias currents.

Claim 7

A diode circuit connected between first and second input terminals of a differential amplifier for providing bias and overload protection, comprising: a first diode having the cathode thereof connected to the first input terminal of the differential amplifier; a second diode having the cathode thereof connected to the anode of said first diode; a third diode having the cathode thereof connected to the anode of said second diode, the anode of said third diode being connected to the second input terminal of the differential amplifier; a fourth diode having the cathode thereof connected to the second input terminal of the differential amplifier; a fifth diOde having the cathode thereof connected to the anode of said fourth diode; a sixth diode having the cathode thereof connected to the anode of said fifth diode, the anode of said sixth diode being connected to the first input terminal of the differential amplifier; conductive means for connecting the junction of said first and second diodes with the junction of said fourth and fifth diodes, said conductive means having a voltage potential applied thereto to normally provide bias current through said second and third diodes to the second input terminal of the differential amplifier and bias current through said fifth and sixth diodes to the first input terminal of the differential amplifier, said first and fourth diodes being normally reversed biased and becoming conductive only when the magnitude of a signal current which may be applied to the amplifier input terminals exceeds the respective bias currents.

Claim 8

A biopotential amplifier of the type wherein the first stage having a first circuit ground and a pair of input terminals adapted to be connected to an external impedance is coupled to a second stage having a second circuit ground and wherein said first and second grounds are electrically isolated from one another, the improvement comprising: oscillator means for generating an alternating signal; a pair of zener diodes connected in series similarly poled, the junction between said pair of diodes being connected to said first circuit ground; means for coupling said oscillator means to the unjoined electrodes of said pair of zener diodes thereby applying said oscillator means alternating signal across said pair of zener diodes whereby the diodes of said pair of zener diodes alternately are forward biased and then reversed biased to their zener breakdown potential, respectively; impedance means for coupling an alternating current from said pair of zener diodes to the input terminals of the amplifier first stage, said impedance means being large in magnitude relative to the external impedance connected between the input terminals whereby said alternating current conducted through said impedance means is proportional to the zener breakdown potential of said pair of zener diodes which current in turn is conducted through the external impedance thereby generating a voltage between the terminals of the first stage proportional to the magnitude of the external impedance connected therebetween.

Claim 9

A biopotential amplifier of the type wherein the first stage having a first circuit ground and a pair of input terminals adapted to be connected to an external impedance is coupled to a second stage having a second circuit ground and wherein said first and second grounds are electrically isolated from one another, the improvement comprising: oscillator means for generating an alternating signal; a pair of zener diodes connected in series similarly poled, the junction between said pair of diodes being connected to said first circuit ground; means for coupling said oscillator means to the unjoined electrodes of said pair of zener diodes thereby applying said oscillator means alternating signal across said pair of zener diodes whereby the diodes of said pair of zener diodes alternately are forward biased and then reversed biased to their zener breakdown potential, respectively; impedance means for coupling an alternating current from said pair of zener diodes to the input terminals of the amplifier first stage, said impedance means being large in magnitude relative to the external impedance connected between the input terminals whereby said alternating current conducted through said impedance means is proportional to the zener breakdown potential of said pair of zener diodes which current in turn is conducted through the external impedance thereby generating a voltage between the terminals of the first stage proportional to the magnitude of the external impedance connected therebetween.

Claim 10

The biopotential amplifier of claim 6 wherein said means for coupling is a transformer.

Claim 11

An impedance pneumograph amplifier for measuring a biological impedance, comprising: a first amplifier stage having a pair of input and output terminals and a first circuit ground, said pair of input terminals being adapted to connect said first amplifier stage to an external biological impedance; a second amplifier stage having an input and an output terminal and a second circuit ground; first coupling means including a modulator, a transformer and a demodulator connected in series between said first amplifier pair of output terminals and said second amplifier input terminal and second circuit ground for electrically isolating said first circuit ground from said second circuit ground and for coupling a signal between said first amplifier output terminals and said second amplifier input terminal and second circuit ground; a pair of zener diodes connected in series and similarly poled, the junction between said pair being connected to said first circuit ground; oscillator means connected to said second circuit ground for generating an alternating signal with respect to said second circuit ground; second coupling means connected between said oscillator means and the unjoined electrodes of said pair of zener diodes for isolating said first and second grounds and for coupling said oscillator means alternating signal to said pair of zener diodes, said pair of zener diodes alternately being forward biased and reversed biased to generate across said pair of zener diodes an alternating voltage having a fixed amplitude determined by the zener voltage of said pair of zener diodes and referenced to said first circuit ground; and third coupling means connected between said pair of zener diodes and said first amplifier pair of input terminals said third coupling means having an impedance magnitude substantially larger than the magnitude of the external biological impedance connected to said pair of input terminals whereby an alternating current proportional to said alternating voltage across said pair of zener diodes is conducted to said input terminals and through said external biological impedance thereby generating a voltage between said input terminals proportional to said external biological impedance connected therebetween.

Claim 12

An impedance pneumograph amplifier for measuring a biological impedance, comprising: a first amplifier stage having a pair of input and output terminals and a first circuit ground, said pair of input terminals being adapted to connect said first amplifier stage to an external biological impedance; a second amplifier stage having an input and an output terminal and a second circuit ground; first coupling means including a modulator, a transformer and a demodulator connected in series between said first amplifier pair of output terminals and said second amplifier input terminal and second circuit ground for electrically isolating said first circuit ground from said second circuit ground and for coupling a signal between said first amplifier output terminals and said second amplifier input terminal and second circuit ground; a pair of zener diodes connected in series and similarly poled, the junction between said pair being connected to said first circuit ground; oscillator means connected to said second circuit ground for generating an alternating signal with respect to said second circuit ground; second coupling means connected between said oscillator means and the unjoined electrodes of said pair of zener diodes for isolating said first and second grounds and for coupling said oscillator means alternating signal to said pair of zener diodes, said pair of zener diodes alternately being forward biased and reversed biased to generate across said pair of zener diodes an alternating voltage having a fixed amplitude determined by the zener voltage of said pair of zener diodes and referenced to said first circuit ground; and third coupling means connected between said pair of zener diodes and said first amplifier pair of input terminals said third coupling means having an impedance magnitude substantially larger than the magnitude of the external biological impedance connected to said pair of input terminals whereby an alternating current proportional to said alternating voltage across said pair of zener diodes is conducted to said input terminals and through said external biological impedance thereby generating a voltage between said input terminals proportional to said external biological impedance connected therebetween.

Claim 13

A circuit of unidirectional devices connected between first and second input terminals of a differential amplifier for providing bias and overload protection, comprising: first and second strings of unidirectional devices connected in series between the input terminals and poled in opposite directions; third and fourth strings of unidirectional devices connected in series between the input terminals and poled in opposite directions, said third and fourth strings being poled opposite to said first and second strings; a fifth string of unidirectional devices connected between the junctions of said first and second strings and said third and fourth strings; and a first and second resistor connected respectively to the junction of said first and second strings and said third and fourth strings, the unconnected ends of said resistors having a voltage potential applied thereacross whereby said first, second and fifth strings are rendered conductive to provide bias to the input terminals, said third and fourth strings being non-conductive until the magnitude of an input signal renders said third and fourth strings conductive and said first and second strings non-conductive thereby providing overload protection.

Claim 14

A circuit of unidirectional devices connected between first and second input terminals of a differential amplifier for providing bias and overload protection, comprising: first and second strings of unidirectional devices connected in series between the input terminals and poled in opposite directions; third and fourth strings of unidirectional devices connected in series between the input terminals and poled in opposite directions, said third and fourth strings being poled opposite to said first and second strings; a fifth string of unidirectional devices connected between the junctions of said first and second strings and said third and fourth strings; and a first and second resistor connected respectively to the junction of said first and second strings and said third and fourth strings, the unconnected ends of said resistors having a voltage potential applied thereacross whereby said first, second and fifth strings are rendered conductive to provide bias to the input terminals, said third and fourth strings being non-conductive until the magnitude of an input signal renders said third and fourth strings conductive and said first and second strings non-conductive thereby providing overload protection.

Claim 15

The circuit of unidirectional devices described in claim 9 wherein said first, second, third, fourth and fifth strings each include one diode.