Noise and overload protection circuit for synchronous demodulators

Claim 2

In a signal processing circuit having an input terminal adapted to receive an input signal and an output terminal at which an output signal is developed, the signal processing circuit tending to provide an output signal of undesired magnitude in response to the magnitude of the input signal exceeding a first threshold level, a protection circuit for controlling the magnitude of the output signal including in combination: voltage reference supply means having an output terminal; first electron control means having a first electrode, a second electrode connected to said output terminal of said voltage reference supply means, and a third electrode; first circuit means coupling said first electrode of said first electron control means to the input terminal of the signal processing circuit, said first electron control means being rendered operative in response to the input signal exceeding a second threshold level which is less than the first threshold level; and second circuit means coupled to said third electrode of said first electron control means and to the output terminal of the signal processing circuit, said second circuit means being responsive to said first electron control means being rendered operative to provide a desired output signal at the output terminal of the signal processing circuit.

Claim 3

The combination of claim 1 wherein said voltage reference supply means includes: a first conductor adapted to apply a power Supply voltage of a first magnitude; a second conductor; first resistive means connected between said first conductor and a circuit node; second resistive means connected between said circuit node and said second conductor; and semiconductor transistor means having a control electrode connected to said circuit node, a first electrode connected to said first conductor and a second electrode forming said output terminal of said voltage reference supply means.

Claim 4

The combination of claim 1 wherein: said first electron control means includes first semiconductor transistor means having a base electrode connected to said output terminal of said voltage reference supply means, said first electrode, and said third electrode; and said first circuit means includes first resistive means connected between said base electrode and said first electrode of said first semiconductor transistor means.

Claim 5

The combination of claim 3 wherein said second circuit means includes: second resistive means connected to said third electrode of said first semiconductor transistor means; second semiconductor transistor means having a control electrode coupled to said first semiconductor transistor means, and an output electrode; and third circuit means coupling said output electrode of said second semiconductor transistor means to the output terminal of the signal processing circuit.

Claim 6

The combination of claim 4 wherein said third circuit means includes a third semiconductor transistor means.

Claim 7

A demodulator circuit suitable for being manufactured in integrated circuit form and for operating at low power supply voltages including in combination: synchronous demodulator means having an input terminal adapted to receive a modulated input signal and an output terminal at which a demodulated output signal is developed, said synchronous demodulator means tending to provide an output signal of undesired magnitude in response to the magnitude of the input signal exceeding a first threshold level; first conductor means adapted to supply a first power supply voltage of a first magnitude; second conductor means; voltage reference supply means connected between said first conductor means and said second conductor means, said voltage reference supply means providing a reference voltage at an output terminal thereof; first electron control means having a first electrode, a second electrode connected to said output terminal of said voltage reference means and a third electrode; first circuit means connecting said first electrode and said second electrode of said first electron control means to said input terminal of said synchronous demodulator means, said first electron control means being rendered conductive in response to the input signal exceeding a second threshold level which is less than said first threshold level; and second circuit means coupled between said third electrode of said first electron control means and said output terminal of said synchronous demodulator means, said second circuit means being responsive to said first electron control means being rendered conductive to provide a desired output signal level at the output terminal of said synchronous demodulator means.

Claim 8

A demodulator circuit suitable for being manufactured in integrated circuit form and for operating at low power supply voltages including in combination: synchronous demodulator means having an input terminal adapted to receive a modulated input signal and an output terminal at which a demodulated output signal is developed, said synchronous demodulator means tending to provide an output signal of undesired magnitude in response to the magnitude of the input signal exceeding a first threshold level; first conductor means adapted to supply a first power supply voltage of a first magnitude; second conductor means; voltage reference supply means connected between said first conductor means and said second conductor means, said voltage reference supply means providing a reference voltage at an output terminal thereof; first electron control means having a first electrode, a second electrode connected to said output terminal of said voltage reference means and a third electrode; first circuit means connecting said first electrode and said second electrode of said first electron control means to said input terminal of said synchronous demodulator means, said first electron control means being rendered conductive in response to the input signal exceeding a second threshold level which is less than said first threshold level; and second circuit means coupled between said third electrode of said first electron control means and said output terminal of said synchronous demodulator means, said second circuit means being responsive to said first electron control means being rendered conductive to provide a desired output signal level at the output terminal of said synchronous demodulator means.

Claim 9

A demodulator circuit suitable for being manufactured in integrated circuit form and for operating at low power supply voltages including in combination: synchronous demodulator means having an input terminal adapted to receive a modulated input signal and an output terminal at which a demodulated output signal is developed, said synchronous demodulator means tending to provide an output signal of undesired magnitude in response to the magnitude of the input signal exceeding a first threshold level; first conductor means adapted to supply a first power supply voltage of a first magnitude; second conductor means; voltage reference supply means connected between said first conductor means and said second conductor means, said voltage reference supply means providing a reference voltage at an output terminal thereof; first electron control means having a first electrode, a second electrode connected to said output terminal of said voltage reference means and a third electrode; first circuit means connecting said first electrode and said second electrode of said first electron control means to said input terminal of said synchronous demodulator means, said first electron control means being rendered conductive in response to the input signal exceeding a second threshold level which is less than said first threshold level; and second circuit means coupled between said third electrode of said first electron control means and said output terminal of said synchronous demodulator means, said second circuit means being responsive to said first electron control means being rendered conductive to provide a desired output signal level at the output terminal of said synchronous demodulator means.

Claim 10

A demodulator circuit suitable for being manufactured in integrated circuit form and for operating at low power supply voltages including in combination: synchronous demodulator means having an input terminal adapted to receive a modulated input signal and an output terminal at which a demodulated output signal is developed, said synchronous demodulator means tending to provide an output signal of undesired magnitude in response to the magnitude of the input signal exceeding a first threshold level; first conductor means adapted to supply a first power supply voltage of a first magnitude; second conductor means; voltage reference supply means connected between said first conductor means and said second conductor means, said voltage reference supply means providing a reference voltage at an output terminal thereof; first electron control means having a first electrode, a second electrode connected to said output terminal of said voltage reference means and a third electrode; first circuit means connecting said first electrode and said second electrode of said first electron control means to said input terminal of said synchronous demodulator means, said first electron control means being rendered conductive in response to the input signal exceeding a second threshold level which is less than said first threshold level; and second circuit means coupled between said third electrode of said first electron control means and said output terminal of said synchronous demodulator means, said second circuit means being responsive to said first electron control means being rendered conductive to provide a desired output signal level at the output terminal of said synchronous demodulator means.

Claim 11

The demodulator circuit of claim 6 wherein: said first electron control means includes first semiconductor transistor means having said first, second and third electrodes; and said first circuit means including a first resistive means connecting said first electrode of said first semiconductor transistor means to said second electrode of said first semiconductor transistor means, said first resistive means cooperating with said voltage reference supply means to render said first semiconductor transistor means conductive in response to said input signal exceeding said second threshold level.

Claim 12

The demodulator circuit of claim 7 wherein: said synchronous demodulator means has first and second input terminals, said first inPut terminal being connected to said first resistive means; said first semiconductor transistor means has first and second emitter electrodes, said first emitter electrode being said first electrode of said first electron control means, and said second emitter electrode comprising a fourth electrode; and said first circuit means further including a second resistive means connecting said second input terminal of said synchronous demodulator means to said second emitter electrode.

Claim 13

The demodulator circuit of claim 6 wherein said second circuit means includes: third resistive means coupled between said third electrode of said first electron control means and said first conductor means; and charge storage means connected between said third electrode of said first electron control means and said first conductor means.

Claim 14

The demodulator circuit of claim 9 wherein said charge storage means is formed by a lateral PNP transistor having emitter, base and collector electrodes.

Claim 15

The demodulator circuit of claim 10 wherein: said base electrode of said lateral PNP transistor is connected to said third electrode of said first electron control means, said emitter electrode of said lateral PNP transistor means is connected to first conductor means; and further including second electron control means having a first electrode connected to said collector of said lateral PNP transistor and a second electrode connected to said output terminal of said synchronous demodulator means.