Current subtractor
AssigneeRCA Corporation
InventorBruce David Rosenthal
Life of this patent
Estimating the term…
Abstract
A current subtractor circuit utilizing a current mirror amplifier (CMA) as the subtracting element. An operational amplifier converts the difference current to an output voltage proportional to this difference. The operational amplifier additionally may be utilized to equalize the voltage drop across the conduction paths of the transistors comprising the CMA and to maintain the CMA output transistor in its constant current region of operation.
Claims10
A circuit for obtaining an output signal proportional to the difference between a first input signal current and a second input signal current comprising, in combination:
- a current mirror amplifier (CMA) having an input terminal to which said first input signal current is applied, an output terminal to which said second input signal current is applied, and a common terminal connected to a point of reference potential;
- a source of bias voltage;
- a differential-input amplifier having an inverting input terminal coupled to said output terminal of said CMA, a non-inverting input terminal connected to said source of bias voltage, and an output terminal from which said output signal can be taken;
- and
- means connecting said differential-input amplifier as a current-to-voltage converter, which means includes
- a direct current feedback path through a resistance connected between said output and said inverting terminals of said amplifier.
In combination:
- first, second and third terminals;
- a current mirror amplifier (CMA) having an input current path and an output current path, said input current path connected between said first and third terminals and said output current path connected between said second and third terminals;
- a differential-input amplifier having inverting and non-inverting signal input terminals, said inverting and non-inverting terminals connected to said second and first terminals respectively;
- and
- means connecting said differential-input amplifier as a current-to-voltage converter, which means includes
- a resistance connected between said inverting and said output terminals.
A subtraction circuit for obtaining an output signal proportional to the difference between a first input signal current and a second input signal current comprising:
- a first terminal for application of a reference potential;
- second and third terminals for application of said first and said second input currents, respectively;
- a fourth terminal from which said output signal is to be available;
- first and second transistors of like type, each having first and second electrodes and a controlled principal conduction path therebetween and having a control electrode, the conduction of its principal conduction path being controlled by the potential between its first and control electrodes;
- means connecting said first and second transistors as a current mirror amplifier, said means including
- connections of the first electrodes of said first and second transistors to said first terminal,
- connections of the second electrodes of said first and said second transistors respectively to said second terminal and to said third terminal,
- an interconnection between the control electrodes of said first and second transistors, and
- means connecting said second terminal to the interconnection between the control electrodes of said first and second transistors, thereby completing a degenerative feedback loop connection that establishes a bias voltage at said second terminal;
- and
- a current-to-voltage converter connecting said third terminal to said fourth terminal, said converter including
- an amplifier having an inverting input terminal connected to said third terminal, having an output terminal connected to said fourth terminal, having a resistance connected between its output and inverting input terminals, and being biased to maintain said third terminal at substantially said bias voltge.
Dependencies are inferred from the claim text.