US 5,210,539 A · Linear frequency sweep synthesizer

Abstract

A circuit for generating an output signal having an output frequency that varies linearly with time, and to an FM CW radar system utilizing such a circuit. The circuit includes a voltage controlled oscillator that produces an output signal at its output terminal at an output frequency that corresponds to the voltage of an input tuning signal. A comparison signal circuit receives the output signal and produces a periodic comparison signal such that when the output frequency varies by .DELTA.f, the comparison signal frequency varies by .DELTA.f/N where N is a positive integer. An update counter periodically causes the value of N to change by a predetermined integer amount. A phase detector compares the comparison signal to a periodic reference signal, and produces a correction signal that is filtered to provide the tuning signal for the VCO. The value of N is preferably changed at an update frequency that is equal to the frequency of the reference signal times an integer. The comparison signal circuit preferably includes a local oscillator for converting the output signal into a periodic IF signal for input to a divider. A high side local oscillator is preferred to minimize loop gain variation with frequency.

Claims18

Dependent claims

A circuit for generating a periodic output signal having an output frequency that varies linearly with time, the circuit comprising:

a voltage controlled oscillator having input and output terminals, and means for producing the output signal at its output terminal at the output frequency such that the output frequency corresponds to the voltage of a tuning signal applied to the input terminal;
a comparison signal generator including division means responsive to the output signal for producing a periodic comparison signal having a comparison frequency such that when the output frequency varies by .DELTA.f, the comparison frequency varies by .DELTA.f/N where N is a positive integer, and update means for periodically causing the value of N to change by a predetermined integer amount as a function of a fixed periodic reference frequency signal;
phase detection means for comparing the comparison signal to the fixed periodic reference frequency signal, and for producing a correction signal corresponding to the difference between the phases of the comparison and reference signals;
and
filter means for filtering the correction signal to produce the tuning signal.

2 more elements

In an FM CW radar system comprising an RF source for producing a periodic output signal having an output frequency that varies linearly with time, an antenna, a mixer having first and second input terminals, means for coupling the output signal to the antenna and to the first input terminal of the mixer, and means for coupling a return signal received at the antenna to the second input terminal of the mixer, whereby the mixer produces a range signal having a frequency corresponding to target range, an improved RF source comprising:

a voltage controlled oscillator having input and output terminals, and means for producing the output signal at its output terminal at the output frequency such that the output frequency corresponds to the voltage of a tuning signal applied to the input terminal;
a comparison signal generator including division means responsive to the output signal for producing a periodic comparison signal having a comparison frequency such that when the output frequency varies by .DELTA.f, the comparison frequency varies by .DELTA.f/N where N is a positive integer, and update means for periodically causing the value of N to change by a predetermined integer amount in response to a fixed periodic reference frequency signal;
phase detection means for comparing the comparison signal to the fixed periodic reference frequency signal, and for producing a correction signal corresponding to the difference between the phases of the comparison and reference signals;
and
filter means for filtering the correction signal to produce the tuning signal.

2 more elements

Dependencies are inferred from the claim text.

Linear frequency sweep synthesizer

Life of this patent

Linear frequency sweep synthesizer

Life of this patent

Abstract

Claims18