US3870968A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Electrometer voltage follower having MOSFET input stage
Assignee: Monroe Electronics Inc
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Filing: 1973-04-09
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Granted: 1975-03-11
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Expires: 1993-04-09
Abstract
Abstract An ultrahigh impedance wide-band voltage follower for use as an electrometer amplifier. The input stage comprises a dual channel MOSFET connected as an amplifier, the first channel having a first gate, source and drain, and the second channel having a second gate, source and drain, the input to the voltage follower being supplied to the first gate. An amplifier is connected to the output of the MOSFET input stage, the output of the amplifier constituting the output of the voltage follower. A connection applies the output of the voltage follower back to the second gate, and a protective circuit having zener conduction and breakdown characteristics is connected between the first gate and the output of the voltage follower to protect the MOSFET input stage when subject to an input overload sufficient to cause destruction of the MOSFET. The voltage follower also includes an intergrator selectively connectible between the protective circuit and the output of the voltage follower operative to integrate a voltage present at the output of the voltage follower due to a residual charge at the input to the voltage follower, and inject a neutralizing current to the input of the voltage follower sufficient to neutralize the residual charge.
Inventors
- 👤 Robert E Vosteen
- 👤 Bruce Theodore Williams
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 09:13
CPC Classifications
H; H03; H03F; H03F3/00; H03F3/45; H03F3/45071; H03F3/45479
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
253 words
An ultrahigh impedance wide-band voltage follower for use as an amplifier comprising, a differentially connected operational amplifier circuit to operate as a voltage follower having an input stage comprising a dual channel MOSFET, the first channel having a first gate, source and drain, and the second channel having a second gate, source and drain, the first and second channels being connected as an amplifier with the input to the voltage follower being supplied to the first gate, and the output from the input stage being at the first and second drains, an amplifier connected to the output of the MOSFET input stage, the output of the amplifier constituting the output of the voltage follower, feedback means to apply the output of the voltage follower back to the second gate, a first protective device having zener conduction and breakdown characteristics, an integrator, and switch means operable to a first condition to connect the first protective device between the first gate and the output of the voltage follower to protect the MOSFET input stage when subject to an input overload sufficient to cause destruction of the MOSFET, and to a second condition to interpose the integrator between the output of the voltage follower and the first protective device to integrate a voltage present at the output of the voltage follower due to a residual charge at the input to the voltage follower, and inject a neutralizing current to the input of the voltage follower through the first protective device sufficient to neutralize the residual charge.
Claim 2
Dependent Claim
253 words
An ultrahigh impedance wide-band voltage follower for use as an amplifier comprising, a differentially connected operational amplifier circuit to operate as a voltage follower having an input stage comprising a dual channel MOSFET, the first channel having a first gate, source and drain, and the second channel having a second gate, source and drain, the first and second channels being connected as an amplifier with the input to the voltage follower being supplied to the first gate, and the output from the input stage being at the first and second drains, an amplifier connected to the output of the MOSFET input stage, the output of the amplifier constituting the output of the voltage follower, feedback means to apply the output of the voltage follower back to the second gate, a first protective device having zener conduction and breakdown characteristics, an integrator, and switch means operable to a first condition to connect the first protective device between the first gate and the output of the voltage follower to protect the MOSFET input stage when subject to an input overload sufficient to cause destruction of the MOSFET, and to a second condition to interpose the integrator between the output of the voltage follower and the first protective device to integrate a voltage present at the output of the voltage follower due to a residual charge at the input to the voltage follower, and inject a neutralizing current to the input of the voltage follower through the first protective device sufficient to neutralize the residual charge.
Claim 3
Dependent Claim
253 words
An ultrahigh impedance wide-band voltage follower for use as an amplifier comprising, a differentially connected operational amplifier circuit to operate as a voltage follower having an input stage comprising a dual channel MOSFET, the first channel having a first gate, source and drain, and the second channel having a second gate, source and drain, the first and second channels being connected as an amplifier with the input to the voltage follower being supplied to the first gate, and the output from the input stage being at the first and second drains, an amplifier connected to the output of the MOSFET input stage, the output of the amplifier constituting the output of the voltage follower, feedback means to apply the output of the voltage follower back to the second gate, a first protective device having zener conduction and breakdown characteristics, an integrator, and switch means operable to a first condition to connect the first protective device between the first gate and the output of the voltage follower to protect the MOSFET input stage when subject to an input overload sufficient to cause destruction of the MOSFET, and to a second condition to interpose the integrator between the output of the voltage follower and the first protective device to integrate a voltage present at the output of the voltage follower due to a residual charge at the input to the voltage follower, and inject a neutralizing current to the input of the voltage follower through the first protective device sufficient to neutralize the residual charge.
Claim 4
Dependent Claim
253 words
An ultrahigh impedance wide-band voltage follower for use as an amplifier comprising, a differentially connected operational amplifier circuit to operate as a voltage follower having an input stage comprising a dual channel MOSFET, the first channel having a first gate, source and drain, and the second channel having a second gate, source and drain, the first and second channels being connected as an amplifier with the input to the voltage follower being supplied to the first gate, and the output from the input stage being at the first and second drains, an amplifier connected to the output of the MOSFET input stage, the output of the amplifier constituting the output of the voltage follower, feedback means to apply the output of the voltage follower back to the second gate, a first protective device having zener conduction and breakdown characteristics, an integrator, and switch means operable to a first condition to connect the first protective device between the first gate and the output of the voltage follower to protect the MOSFET input stage when subject to an input overload sufficient to cause destruction of the MOSFET, and to a second condition to interpose the integrator between the output of the voltage follower and the first protective device to integrate a voltage present at the output of the voltage follower due to a residual charge at the input to the voltage follower, and inject a neutralizing current to the input of the voltage follower through the first protective device sufficient to neutralize the residual charge.
Claim 5
Dependent Claim
17 words
An ultrahigh impedance voltage follower as recited in claim 1 wherein the amplifier comprises an operational amplifier.
Claim 6
Dependent Claim
37 words
An ultrahigh impedance voltage follower as recited in claIm 1 further comprising, means to bootstrap circuit the first and second drains to the output of the voltage follower to reduce the input capacitance of the voltage follower.
Claim 7
Dependent Claim
40 words
An ultrahigh impedance voltage follower as recited in claim 3 further comprising, a probe housing the input stage, a driven shield surrounding the probe housing to drive the input capacitance in conjunction with the bootstrap connection to a negligible value.
Claim 8
Dependent Claim
52 words
An ultrahigh impedance voltage follower as recited in claim 4 further comprising, a shield connected to a common connection of the voltage follower functioning as a convenient ground connection for low level input signals and as a positive shield should the output of the input stage be subject to gross external interference.
Claim 9
Dependent Claim
48 words
An ultrahigh impedance voltage follower as recited in claim 1 wherein the integrator output capability exceeds the zener breakdown rating of the first protective device to insure rapid discharge of any residual charge at the input to the voltage follower through zener conduction of the first protective device.
Claim 10
Dependent Claim
49 words
An ultrahigh impedance voltage follower as recited in claim 6 further comprising, a second protective device including a double zener diode connected to function as a double anode zener diode connectible across the integrator when the means operable between first and second conditions are operated to the second condition.
Claim 11
Dependent Claim
30 words
An ultrahigh impedance voltage follower as recited in claim 7 wherein the zener breakdown voltage of the second protective device slightly exceeds the breakdown voltage of the first protective device.
Claim 12
Dependent Claim
52 words
An ultrahigh impedance voltage follower as recited in claim 1 further comprising, means to intentionally introduce a small voltage offset error between the voltage follower input and output to correspondingly introduce a current into the voltage follower input through the first protective device that is equal to the first gate input current.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-03-10 | 1978-09-09 | 1979-03-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-10 | 1982-09-09 | 1983-03-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-10 | 1986-09-09 | 1987-03-11 | $7700.00 | Window Closed / Lapsed |