Amplifiers – With semiconductor amplifying device – Including combined diverse-type semiconductor device
Patent
1982-09-20
1985-01-08
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including combined diverse-type semiconductor device
330262, 330292, 330311, 330156, H03F 138, H03F 316
Patent
active
044929323
ABSTRACT:
An electronic circuit for a high impedance probe for an instrument for measuring electrical voltages, comprising an input field effect transistor 15 connected in a source-follower configuration, a bipolar transistor 17 connected in an emitter-follower configuration and controlled by the transistor 15, a current source 18 serving as a load for the transistor 17, an amplifier 19 having a gain G which is slightly less than unity, the input of the amplifier being controlled by the transistor 15, and finally a resistor 20 which serves as a load for the transistor 15 and which connects the source of the transistor 15 to the output 8 of the amplifier 19, said output also serving as the output of the circuit, which is supplied by a voltage source applied between the current source 18 and the collector of the transistor 17. By virtue of the amplifier 19, the effective load resistance seen by the transistor 15 is R.sub.20 /(1-G), R.sub.20 being the value of the resistor 20. If G is slightly less than unity, a substantial effective load resistance can be obtained with a low value in respect of the resistor 20. The d.c. voltage drop in the resistor 20 will thus be low, which permits the circuit to be supplied at a low voltage and to dissipate a small amount of energy, which represents the main aim sought by the present invention.
REFERENCES:
patent: 3436672 (1969-04-01), Delagrange
patent: 3995175 (1976-11-01), Hoyt et al.
Maddox, H. L., "High Input Impedance Capacitance Coupled Voltage Probes", Western Electric Technical Digest No. 45, Jan. 1977, pp. 27-29.
Asulab S.A.
Mullins James B.
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