Differential amplifier circuit

Claim 2

A circuit for periodically balancing the amplifying elements of a differential amplifier, comprising: means for periodically inducing predetermined signal levels on the inputs of each of said amplifying elements; means responsive to said periodically inducing means and an output of said differential amplifier for sensing an imbalance between said amplifying elements while said predetermined signal levels are induced on said inputs; means responsive to said sensing means for changing the gain of said differential amplifier to correct for said imbalance; and means for maintaining the corrected gain of said differential amplifier during the periods between successive operations of said periodically inducing means.

Claim 3

The circuit defined in claim 1 wherein said maintaining means comprises: means for averaging the output signal of said gain changing means over a period greater than the period of said periodically inducing means, and means for regulating the gain of said one of said amplifying elements in accordance with the output of said averaging means.

Claim 4

The circuit defined in claim 2 wherein said means for averaging the output signal comprises a capacitor charged by the output of said gain changing means through a resistor.

Claim 5

The circuit defined in claim 3 wherein said regulating means comprises a transistor connected to limit the current through one of said amplifying elements in response to the charge level of said capacitor.

Claim 6

The circuit defined in claim 1 wherein said predetermined signal level is zero volts, and wherein said periodically inducing means induces ground potentials on the inputs of each of said amplifying elements.

Claim 7

A circuit for periodically balancing the amplifying elements of a differential amplifier, comprising: an energy storage device; means for periodically altering the energy level of said energy storage device in accordance with the imbalance of said amplifying elements; and means connected to the output of one of said amplifying elements for limiting the output current of said one of said amplifying elements in response to the energy level of said energy storage device.

Claim 8

A circuit for periodically balancing the amplifying elements of a differential amplifier, comprising: an energy storage device; means for periodically altering the energy level of said energy storage device in accordance with the imbalance of said amplifying elements; and means connected to the output of one of said amplifying elements for limiting the output current of said one of said amplifying elements in response to the energy level of said energy storage device.

Claim 9

The circuit defined in claim 6 wherein said altering means comprises: means for periodically inducing predetermined signals upon the inputs of each of said amplifying elements, and means for changing said energy level in accordance with said imbalance only during said periodic inducing.

Claim 10

The circuit defined in claim 7 wherein said predetermined signals are equal.

Claim 11

The circuit defined in claim 7 wherein said energy level altering means introduces only a predetermined change in said energy level during any one period of said periodically inducing means, said predetermined change being insufficient to correct for large circuit imbalances.

Claim 12

A circuit for periodically correcting the imbalance of a differential amplifier which includes amplifying elements the amplification characteristics of which may vary by a substantial amount, such as field effect transistors, comprising: means for periodically monitoring circuit imbalance; and means responsive to said monitoring means for automatically correcting said circuit imbalance, said correcting means introducing a predetermined amount of correction for said circuit imbalance during each period of said periodically monitoring means, said predetermined amount being insufficient to correct for large circuit imbalances.

Claim 13

A circuit for periodically correcting the imbalance of a differential amplifier which includes amplifying elements the amplification characteristics of which may vary by a substantial amount, such as field effect transistors, comprising: means for periodically monitoring circuit imbalance; and means responsive to said monitoring means for automatically correcting said circuit imbalance, said correcting means introducing a predetermined amount of correction for said circuit imbalance during each period of said periodically monitoring means, said predetermined amount being insufficient to correct for large circuit imbalances.

Claim 16

The method defined in claim 11 wherein said sensing step comprises: inducing a predetermined signal on the inputs of said amplifying elements once during each period of said periodic clock pulse; and sensing imbalance of said amplifying elements during the times when said predetermined signal is induced on said inputs.

Claim 17

A circuit for correcting the imbalance of a differential amplifier, comprising: a clocking circuit for producing a periodic output signal; means responsive to said clocking circuit for periodically grounding the inputs to said differential amplifier; a voltage sensing circuit responsive to an output of said differential amplifier for producing an output signal representative of the imbalance of said differential amplifier; a capacitor; means responsive to said output of said clocking circuit and said output of said voltage sensing circuit for charging or discharging said capacitor in accordance with said output of said voltage sensing circuit only when said periodically grounding means is grounding said inputs; and means for altering the gain of said differential amplifier in accordance with the charge on said capacitor.

Claim 18

A circuit for correcting the imbalance of a differential amplifier, comprising: a clocking circuit for producing a periodic output signal; means responsive to said clocking circuit for periodically grounding the inputs to said differential amplifier; a voltage sensing circuit responsive to an output of said differential amplifier for producing an output signal representative of the imbalance of said differential amplifier; a capacitor; means responsive to said output of said clocking circuit and said output of said voltage sensing circuit for charging or discharging said capacitor in accordance with said output of said voltage sensing circuit only when said periodically grounding means is grounding said inputs; and means for altering the gain of said differential amplifier in accordance with the charge on said capacitor.

Claim 19

A circuit for maintaining the amplifying elements of a differential amplifier in a balanced condition, comprising: means for maintaining a reference signal; means connected to the output of one of said amplifying elements for limiting the output current of said one of said amplifying elements in accordance with said reference signal; means for measuring the imbalance of said differential amplifier; and means of resetting said reference signal periodicially in response to said measuring means.

Claim 20

A circuit for maintaining the amplifying elements of a differential amplifier in a balanced condition, comprising: means for maintaining a reference signal; means connected to the output of one of said amplifying elements for limiting the output current of said one of said amplifying elements in accordance with said reference signal; means for measuring the imbalance of said differential amplifier; and means of resetting said reference signal periodicially in response to said measuring means.

Claim 21

A circuit as defined in claim 14 wherein said maintaining means comprises a capacitor, and wherein said means for resetting charges or discharges said capacitor with a limited current for a limited length of time.

Claim 22

A circuit defined in claim 15 wherein said current limiting means comprises: a semiconductor, the impedance of which is responsive to the charge on said capacitor, said semiconduCtor series connected with said output of said one of said amplifying elements.