Claims
- 1. A differential amplifier, comprising:
- a differential input stage having differential voltage inputs with said inputs connected to amplifiers with output terminals connected through a resistor at respective current feedback inputs, and
- a current clamp comprising:
- a comparison circuit connected to said differential input terminal to compare the voltage across said input terminals to a threshold value, comprising
- (i) a differential pair of transistors having a tail current, and
- (ii) a threshold circuit, said threshold circuit connected to provide voltages at the control terminals of said differential pair representative of a differential voltage appearing across the input terminals of said amplifier, with a threshold voltage added to said input differential input voltage, and
- a current diverting circuit connected to divert said amplifier's bias current and to be controlled in said diversions by said comparison circuit.
- 2. The differential amplifier of claim 1, wherein said threshold circuit and differential pair are connected to divert the tail current of said differential pair from the bias current source of said amplifier whenever the differential input voltage exceeds said threshold voltage.
- 3. The differential amplifier of claim 2, said input stage including a plurality of bipolar output transistors, wherein said current clamp further comprises a reverse biasing circuit connected to reverse bias the base-emitter junctions of said transistors when the differential input voltage exceeds said threshold voltage.
- 4. A subranging analog-to-digital converter comprising:
- a sample and hold circuit connected to receive and hold a differential analog signal,
- an analog-to-digital converter connected to receive the held analog signal from said sample and hold circuit and to convert said analog signal to a digital signal,
- a digital to analog converter connected to convert said digital signal from the analog to digital converter into an analog signal,and
- a differential amplifier connected to receive analog signals from said sample and hold circuit and from said digital to analog converter and to produce an analog signal based upon those inputs, said amplifier comprising:
- a differential input stage having differential voltage inputs with said inputs connected to amplifiers whose outputs are connected through a resistor at respective current feedback inputs, and
- a current clamp comprising:
- a comparison circuit connected to said differential input terminals to compare the voltage across said input terminals to a threshold value, and
- a current diverting circuit connected to divert said amplifier's bias current and to be controlled in said diversion by said comparison circuit.
- 5. The subranging analog-to-digital converter of claim 4, wherein said comparison circuit comprises:
- a differential pair of transistors having a tail current, and
- a threshold circuit, said threshold circuit connected to provide voltages at the control terminals of said differential pair representative of a differential voltage appearing across the input terminals of said amplifier, with a threshold voltage added to said input differential input voltage.
- 6. The subranging analog-to-digital converter of claim 5, wherein said threshold circuit and differential pair are connected to divert the tail current of said differential pair from the bias current source of said amplifier whenever the differential input voltage exceeds said threshold voltage.
- 7. The subranging analog-to-digital converter of claim 6, said input stage including a plurality of bipolar output transistors, wherein said current clamp further comprises a reverse biasing circuit connected to reverse bias the base-emitter junctions of said transistors when the differential input voltage exceeds said threshold voltage.
- 8. A differential amplifier, comprising:
- a differential input stage having differential voltage inputs with said inputs connected to amplifiers whose output terminals are connected through a resistor at respective current feedback inputs, and
- a clamp circuit connected to divert bias current from the input stage when the voltage across the differential inputs exceeds a threshold value, wherein said clamp circuit includes a comparison circuit connected to said differential input terminals to compare the voltage across said input terminals to a threshold value, and a current diverting circuit connected to divert said amplifier's bias current and to be controlled in said diversion by said comparison circuit, wherein said comparison circuit comprises:
- a differential pair of transistors having a tail current, and
- a threshold circuit, said threshold circuit connected to provide voltages at the control terminals of said differential pair representative of a differential voltage appearing across the input terminals of said amplifier, with a threshold voltage added to said input differential input voltage.
- 9. A method of protecting a differential amplifier from excessive input signals comprising:
- sensing the amplifier's input signal,
- in response to the sensed input signal exceeding a predetermined safe threshold value, diverting bias current from said amplifier to prevent it being damaged, and
- reverse biasing the base emitter junctions of transistors within the amplifier in response to sensed input signals exceeding a predetermined safe threshold value.
GOVERNMENT RIGHTS
This invention was made with U.S. government support, and the government has certain rights in the invention.
US Referenced Citations (5)