US 6,646,500 B2 · Integrated circuit having an FM demodulator and method therefor

Abstract

A digital FM demodulator employs a baseband phase lock loop (BBPLL), which is particularly effective for long range reception, for combining and demodulating a pair of signals represented by the mathematical expression A(t)ejθ(t) to result in an approximation of dθ/dt. This approximation is then subjected to an inverse of the linear approximation of the frequency response of the BBPLL that produces a very accurate θ. This is conveniently achieved with a IIR filter whose transfer function happens to be the same as the inverse of the linear approximation of the frequency response of the BBPLL. The derivative is then taken of θ to produce a very accurate dθ/dt, the desired result for the output of an FM demodulator. To aid operation of the BBPLL, the incoming digital intermediate frequency is upsampled by a combination of sample and hold and FIR filtering prior to being processed by the BBPLL.

Claims20

Dependent claims

An integrated circuit, comprising:

a digital automatic gain control (AGC) circuit for receiving a filtered intermediate frequency (IF) signal, and in response, providing a gain-controlled IF signal;
an upsampler for receiving the gain-controlled IF signal, and for providing an upsampled signal;
a digital phase-locked loop for receiving the upsampled signal, and in response, providing a demodulated signal;
and
a compensation circuit for receiving the demodulated signal, and in response, reducing a distortion in the demodulated signal to produce a distortion-reduced demodulated signal.

2 more elements

A method for demodulating a frequency modulated (FM) signal, comprising the steps of:

receiving a filtered intermediate frequency (IF) signal;
providing a gain-controlled IF signal using an automatic gain control (AGC) circuit at a first sample rate;
upsampling the gain-controlled IF signal to provide an upsampled signal at a second sample rate greater than the first sample rate;
demodulating the upsampled signal using a digital phase-locked loop (PLL) to produce a demodulated signal;
and
compensating for a distortion in the demodulated signal to produce a distortion-reduced demodulated signal.

3 more elements

Dependencies are inferred from the claim text.

Integrated circuit having an FM demodulator and method therefor

Life of this patent

Integrated circuit having an FM demodulator and method therefor

Life of this patent

Abstract

Claims20