National Semiconductor Corporation

Tim D Isbell

Walter R Davis

Don Roy Sauer

Robert C Dobkin

James S Congdon

Bernard D Miller

Lawrence R Sample

A circuit for pulse width modulating the output of a voltage controlled oscillator without introducing any ocillator frequency or amplitude (slope) modulation. A summing circuit is combined with a comparator and provided with inputs that accommodate differential sum/difference inputs, an error input and a ramp input from the oscillator or other source. The ramp and error signals are combined differentially to pulse width modulate the comparator output and pulse width modulation can also be achieved by via the sum/difference inputs a differential relationship.

Pulse width modulator circuit for switching regulators

A circuit is shown for pulse width modulating the output of a voltage controlled oscillator without introducing any oscillator frequency or amplitude (slope) modulation. A summing circuit is combined with a comparator and provided with inputs that accommodate differential sum/difference inputs, an error input and a ramp input from the oscillator or other source. The ramp and error signals are combined differentially to pulse width modulate the comparator output and pulse width modulation can also be achieved via the sum/difference inputs in a differential relationship.

In an AM stereo radio receiver, a pilot signal is recovered from the phase modulated channel. The pilot signal is sensed by means of a bandpass filter tuned to the subaudible signal frequency and is used to operate a detector-switching amplifier combination. The switching amplifier actuates a visual indicator which shows the presence of a stereo broadcast. The receiver is provided with an electronic blend function that operates in response to the pilot signal and an excess phase signal that is present when the receiver is mistuned. OR Logic, which responds to either mistuning or a lack of stereo pilot signal, switches the receiver to monaural response. If desired, further OR Logic can include response to weak signals, in which case an improvement in signal to noise ratio is achieved.

AM Stereo receiver logic

In an amplifier circuit the output devices are thermally coupled to a shutdown circuit. A first latch is designed to operate at a first high temperature excursion. The first latch operation acts to shut the output devices off and to invoke a second latch. The second latch operates between a low temperature and a second high temperature that is below the first high temperature. Thus, after the first latch operates, the second latch will operate to cycle between a low temperature whereupon it energizes the output devices and a high temperature at which it deenergizes the output devices. By this action, the circuit will permit only one high temperature peak after which it will cycle between a lower high temperature peak and a low temperature. This avoids repeated cycling to a high temperature that could be deleterious to the circuit devices or the package in which they are housed.

Two stage thermal shutdown

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.

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San Jose, CA, United States of America

Tim D Isbell