Dark current compensating circuit

Claim 2

A circuit for suppressing the effect of a given electrical signal which is relatively constant over a determined time period comprising: a. a first circuit means having an output terminal, a fixed potential input terminal, and a conductive path for said electrical signal from said input terminal to said output terminal; b. an amplifying means, the input of which is coupled to said output terminal of said circuit means; c. a capacitive means coupled to the output of said amplifying means, said amplifying means being adapted to bias said capacitive means during a first portion of said time period; d. an isolating means disposed between said output terminal and said capacitive means and isolating said capacitive means from said output terminal during a second portion of said time period; and e. a second circuit means coupled between said capacitive means and said input terminal of said first circuit means and providing a flow path between said capacitive means and said input terminal at least during said second porTion of said time period, whereby the magnitude of the electrical signal at said output terminal resulting from said given electrical signal is reduced at least during said second portion of said time period.

Claim 3

The circuit of claim 1 wherein: a. said input of said amplifying means is connected to said output terminal; and b. said isolating mean is connected between and provides a conductive path between said output of said amplifying means and said capacitive mean during said first portion of said time period and isolates said capacitive means from said output of said amplifying means during said second portion of said time period.

Claim 4

The circuit of claim 2 wherein said first circuit means is an operational amplifier having a resistive feedback.

Claim 5

The circuit of claim 2 wherein said second circuit means is adapted to provide a flow path between said input terminal and said capacitive means during said first and second portions of said time period and said amplifying means is adjustable such that the potential at said output terminal can be set substantially equal to the potential at said input terminal during said first portion of said time period.

Claim 6

The circuit of claim 2 wherein said amplifying means is adapted to charge and discharge said capacitive mean during said first portion of said time period in response to fluctuations in said given electrical signal such that the bias charge on said capacitive means is determined by the average value of said given electrical signal.

Claim 7

The circuit of claim 5 wherein said capacitive means comprises a short term memory and a long term memory, said short term memory adapted to respond rapidly to said fluctuations and said long term memory adapted to predominate thereby controlling the bias on said capacitive means.

Claim 8

A circuit for suppressing the effect of the average value of a given electrical signal, the average being relatively constant over a determined time period, said given electrical signal being present alone during a first portion of said time period and in combination with at least one other electrical signal during a second portion of said time period, said circuit comprising: an operational amplifier having an output terminal and a fixed potential input terminal, resistance feedback connected between said output and input terminals, an adjustable amplifying means connected to said output terminal, a capacitive means coupled to said amplifying means, said amplifying means adapted to charge and discharge said capacitive means during only said first portion of said time period in response to fluctuations in said given electrical signal such that the bias charge on said capacitive means is determined by the average value of said given electrical signal, and resistive means coupled between said capacitive means and said input terminal of said operational amplifier, said resistive means selected such that by adjustment of said adjustable amplifying means, an electrical signal substantially equal to the average of said given electrical signal will flow between said input terminal and said capacitive means during said time period.

Claim 9

A circuit for suppressing the effect of the average value of a given electrical signal, the average being relatively constant over a determined time period, said given electrical signal being present alone during a first portion of said time period and in combination with at least one other electrical signal during a second portion of said time period, said circuit comprising: an operational amplifier having an output terminal and a fixed potential input terminal, resistance feedback connected between said output and input terminals, an adjustable amplifying means connected to said output terminal, a capacitive means coupled to said amplifying means, said amplifying means adapted to charge and discharge said capacitive means during only said first portion of said time period in response to fluctuations in said given electrical signal such that the bias charge on said capacitive means is determined by the average value of said given electrical signal, and resistive means coupled between said capacitive means and said input terminal of said operational amplifier, said resistive means selected such that by adjustment of said adjustable amplifying means, an electrical signal substantially equal to the average of said given electrical signal will flow between said input terminal and said capacitive means during said time period.

Claim 10

The circuit of claim 7 wherein said amplifying means includes a pair of transistors connected together through their base terminals and through one other terminal of such that said pair of transistors are alternately driven conductive and nonconductive during said first portion of said time period in response to fluctuations in said given electrical signal, and a control transistor having the conductive path formed by its collector and emitter terminals coupled between said base terminals and said other terminals of said pair of transistors, said control transistor being adapted to turn off said pair of transistors during said second portion of said time period.

Claim 11

The circuit of claim 7 wherein said capacitive means comprises a short term memory and a long term memory, said short term memory adapted to respond rapidly to said fluctuations and said long term meMory adapted to predominate thereby controlling the bias on said capacitive means.

Claim 12

The circuit of claim 9 wherein said short term memory is a low value capacitor and said long term memory is high value capacitor in combination with a resistor.

Claim 17

A circuit for suppressing the effect of the average value of a given electrical signal, the average being relatively constant over a determined time period, said given electrical signal being present alone during a first portion of said time period and in combination with at least one other electrical signal during a second portion of said time period, said circuit comprising: a. an operational amplifier having an output terminal and a fixed potential input terminal; b. a resistance feedback connected between said output and input terminals; c. an adjustable amplifying means, the input of which is coupled to said output terminal; d. a capacitive means coupled to the output of said adjustable amplifying means; e. an isolating means disposed between said output terminal and said capacitive means, during said first portion of said time period and isolating said capacitive means from said output terminal during said second portion of said time period, said amplifying means adapted to bias said capacitive means during said first portion of said time period; and f. a resistive means coupled between said capacitive means and said input terminal of said operational amplifier, said resistive means selected such that by adjustment of said adjustable amplifying means an electrical signal substantially equal to the average of said given electrical signal will flow between said input terminal and said capacitive means during said time period.

Claim 18

A circuit for suppressing the effect of the average value of a given electrical signal, the average being relatively constant over a determined time period, said given electrical signal being present alone during a first portion of said time period and in combination with at least one other electrical signal during a second portion of said time period, said circuit comprising: a. an operational amplifier having an output terminal and a fixed potential input terminal; b. a resistance feedback connected between said output and input terminals; c. an adjustable amplifying means, the input of which is coupled to said output terminal; d. a capacitive means coupled to the output of said adjustable amplifying means; e. an isolating means disposed between said output terminal and said capacitive means, during said first portion of said time period and isolating said capacitive means from said output terminal during said second portion of said time period, said amplifying means adapted to bias said capacitive means during said first portion of said time period; and f. a resistive means coupled between said capacitive means and said input terminal of said operational amplifier, said resistive means selected such that by adjustment of said adjustable amplifying means an electrical signal substantially equal to the average of said given electrical signal will flow between said input terminal and said capacitive means during said time period.

Claim 19

The circuit of claim 13 wherein: a. said input of said amplifying means is connected to said output terminal; and amplifying b. said isolating means is connected between and provides a conductive path between said output of said adjustable amplifying mEans and said capacitive means, during said first portion of said time period and isolating said capacitive means from said adjustable amplifying means during said second portion of said time period, said amplifying means adapted to bias said capacitive means during only said first portion of said time period.