Tuned inductorless active phase shift demodulator
AssigneeMotorola, Inc.
InventorsWalter L. Davis, Yolanda Prieto
Life of this patent
Estimating the term…
Abstract
An inductorless quadrature demodulator for frequency modulated signals is disclosed. A limited FM signal is passed through an active filter (26) and a phase shift network (30) to produce a quadrature signal. The limited FM signal is compared with the quadrature signal in an EXCLUSIVE OR gate (24) and then low pass filtered (36) to obtain recovered audio. The active filter (26) includes a transconductance amplifier (60) whose center frequency can be adjusted by appropriate adjustment of the amplifier's bias current. The bias current is temperature compensated to allow operation of the demodulator over a wide temperature range.
Claims23
An inductorless quadrature demodulator for demodulating a frequency modulated (FM) signal which deviates in frequency about a center frequency, comprising:
- inductorless active phase shifting means receiving said FM signal, for shifting the phase of said FM signal linearly over a predetermined range of frequencies about said center frequency to produce a quadrature signal, said inductorless active phase shifting means having a Q factor greater than 1;
- frequency adjusting means, coupled to said inductorless active phase shifting means, for adjusting the frequency at which said quadrature signal is produced;
- and
- phase detecting means, having an output node, for detecting a difference in phase between said FM signal and said quadrature signal and for producing a signal varying with said difference in phase at said output node.
A quadrature demodulator for demodulating a frequency modulated (FM) signal which deviates in frequency about a center frequency, comprising:
- an active filter having an input for receiving said FM signal and an output, said active filter having a Q greater than 1 and providing linear phase shift over a range of frequencies centered about said center frequency;
- a constant phase shift network coupled to said output of said active filter for providing a constant phase shift of approximately 90 degrees over said predetermined range of frequencies, said constant phase shift network producing in conjunction with said active filter a quadrature signal;
- frequency adjusting means, coupled to said active filter, for adjusting the frequency at which said quadrature signal is produced;
- an EXCLUSIVE OR gate having two inputs and an output, one of said inputs receiving said FM signal and the other of said inputs receiving said quadrature signal;
- and
- a low pass filter coupled to said output of said EXCLUSIVE OR gate.
A method of demodulating a frequency modulated (FM) signal which is deviated in frequency about a center frequency, comprising the steps of:
- shifting the phase of said FM signal without an inductor by approximately 180 degrees at said center frequency and shifting the phase of said FM signal linearly within a predetermined range of frequencies about said center frequency to produce a shifted signal;
- applying a constant phase shift of approximately 90 degrees in a direction opposite to the direction of shift of 180 degrees to said shifted signal for all frequencies within said predetermined range to produce in conjunction with said linear phase shift of approximately 180 degrees a quadrature signal;
- adjusting the frequency at which said quadrature signal is produced;
- and
- detecting the phase difference between said FM signal and said quadrature signal.
A method of fabricating an integrated circuit frequency modulated (FM) demodulator, comprising the ordered steps of:
- A. processing an integrated circuit including an inductorless FM demodulator having an active phase shifting means including an active filter;
- B. applying electrical energy to said integrated circuit;
- C. monitoring an audio characteristic of said demodulator while adjusting the resonant frequency of said active phase shifting means to effect tuning of said demodulator;
- and
- D. packaging said integrated circuit.
An inductorless demodulator for demodulating a frequency modulated (FM) signal which deviates in frequency about a center frequency, comprising:
- inductorless active phase shifting means receiving said FM signal, for shifting the phase of said FM signal linearly over a predetermined range of frequencies about said center frequency to produce a shifted signal;
- frequency adjusting means, coupled to said active phase shifting means, for adjusting the frequency at which said quadrature signal is produced;
- and
- phase detecting means, having an output node, for detecting predetermined differences in phase between said FM signal and said shifted signal and for producing a signal varying with said difference in phase at said output node.
Dependencies are inferred from the claim text.