Amplifiers – With semiconductor amplifying device – Including differential amplifier
Patent
1979-02-05
1980-11-04
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including differential amplifier
330257, 330259, 330260, 330261, H03F 345
Patent
active
042322715
ABSTRACT:
In an instrumentation amplifier a differential input is provided, one side of which is connected to an instrument ground that is remote from the amplifier power supply ground. The remote ground can, under some conditions, operate at a potential that is outside the potential span of the amplifier power supply. Such common mode potentials are difficult to cope with when the difference exceeds about 0.6 volt. The circuit employs a pair of transistors biased to equal current densities. The emitters constitute the circuit input terminals. Means are provided to adjust the transistor collector to base voltage to establish a constant predetermined current. The transistor that is to be connected to the remotely grounded input has a resistor coupled between emitter and base to produce a reference current. A resistor connected between the transistor bases will then assume a potential equal to the emitter potential difference. A current mirror reproduces the base resistor current at the amplifier output terminal. Since the transistor emitters can operate at several volts below ground, an extended common mode range is available.
REFERENCES:
patent: 4004247 (1977-01-01), Van de Plassche
Dobkin Robert C.
Isbell Tim D.
Miller Bernard D.
Sample Lawrence R.
Mullins James B.
National Semiconductor Corporation
Woodward Gail W.
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