Automatic noise limiter
First Claim
1. An automatic noise limiter circuit for use in a radio frequency receiver, the receiver producing a high frequency signal which is amplitude modulated by an audio signal, the automatic noise limiter comprising:
- peak detector means for rectifying and filtering the amplitude modulated high frequency signal to recovere the audio signal therefrom and produce a direct current signal representative of the magnitude of the high frequency signal;
low pass filter means for processing the recovered audio signal and the direct current signal from the peak detector means and producing at its output a representative direct current level;
high pass filter means for passing to its output a predetermined portion of the recovered audio signal from the peak detector means, the high pass filter means preventing the peak detector means produced direct current level from passing to its output;
a noise limiter output terminal;
switch means comprising a semiconductor rectifier coupled between the output of the low pass filter and the output of the high pass filter, the rectifier exhibiting a low impedance response to the low filter output exceeding the high pass filter output by a predetermined threshold level, the rectifier otherwise exhibiting a high impedance;
a bias means coupled to the semiconductor rectifier for producing zero bias across said rectifier in the absence of a high frequency signal from the receiver said bias means comprising temperature compensating means for maintaining said rectifier at zero bias over a temperature range in the absence of a high frequency signal from the receiver.
0 Assignments
0 Petitions
Accused Products
Abstract
The output from a peak detector of a conventional radio receiver includes a recovered audio signal and a DC level. The disclosed noise limiter processes the detector output through both low pass and high pass filters. The low pass filter produces a DC signal representative of both the detector DC level and the recovered audio signal level. The high pass filter passes only the recovered audio signal. A semiconductor diode connects between the filter outputs, and the output of the noise limiter. For peak detector levels at, or below the 100% modulation level the diode is forward biased and passes the audio signal to the noise limiter output for further receiver processing. Peak detector levels exceeding 100% modulation, such as noise, reverse bias the diode whereby the audio signal is blocked from subsequent receiver stages.
-
Citations
5 Claims
-
1. An automatic noise limiter circuit for use in a radio frequency receiver, the receiver producing a high frequency signal which is amplitude modulated by an audio signal, the automatic noise limiter comprising:
-
peak detector means for rectifying and filtering the amplitude modulated high frequency signal to recovere the audio signal therefrom and produce a direct current signal representative of the magnitude of the high frequency signal; low pass filter means for processing the recovered audio signal and the direct current signal from the peak detector means and producing at its output a representative direct current level; high pass filter means for passing to its output a predetermined portion of the recovered audio signal from the peak detector means, the high pass filter means preventing the peak detector means produced direct current level from passing to its output; a noise limiter output terminal; switch means comprising a semiconductor rectifier coupled between the output of the low pass filter and the output of the high pass filter, the rectifier exhibiting a low impedance response to the low filter output exceeding the high pass filter output by a predetermined threshold level, the rectifier otherwise exhibiting a high impedance; a bias means coupled to the semiconductor rectifier for producing zero bias across said rectifier in the absence of a high frequency signal from the receiver said bias means comprising temperature compensating means for maintaining said rectifier at zero bias over a temperature range in the absence of a high frequency signal from the receiver. - View Dependent Claims (2, 3, 4, 5)
-
Specification