Amplitude locked loop circuits

Details Amplitude locked loop circuits Amplitude locked loop circuits

1992-07-22

1994-08-23

Mullins, James B.

Demodulators

Frequency modulation demodulator

Having specific distortion, noise or other interference...

329325, 329350, 329353, 455260, 455312, H03D 118, H04B 110

Patent

active

053411064

DESCRIPTION:

BRIEF SUMMARY
This invention relates to electronic circuits, and more particularly to electronic circuits having loop-locked amplitude control.
In 1933 De Bellicise in France invented a category of circuitry generally called the Phase Locked Loop (PLL). Although a number of decades elapsed before the PLL was fully understood it is now used as a basic building block in many telecommunications, computer and consumer products. Two primary applications, for example, of the use of the PLL would be in the recovery of the data from all disc drives and for the recovery of audio signal from frequency modulated signals.
Similar to the PLL there is a category of circuitry called automatic gain control (AGC) which was invented in the mid-twenties of this century. Although AGC has been applied for many years it has never been fully explained in a clear analytical manner--many of the papers and patents being based on an ad-hoc approach to design problems associated with this circuitry.
This invention concerns a new category of circuitry which will be hereafter referred to as the Amplitude Locked Loop (ALL) since it embodies all the principles of the PLL but operates in the amplitude domain or real domain and not in the frequency or imaginary domain. The ALL will be described as the dual of PLL.
According to the present invention there is provided an electronic circuit having loop-locked amplitude control, said circuit comprising a voltage-controlled amplifier coupled to receive a circuit input signal and a feedback signal, a modulus detector whose input is coupled to the output of the voltage-controlled amplifier, and an integrator whose input is coupled to the output of the modulus detector, the output of the integrator being coupled to the voltage-controlled amplifier to deliver said feedback signal thereto, whereby said electronic circuit forms an amplitude locked loop with the output of the integrator providing the output signal of the circuit.
Said voltage-controlled amplifier is preferably constituted by a linear signal multiplier.
Said modulus detector is preferably constituted by a full-wave precision rectifier.
The output of the modulus detector is preferably coupled to the input of the integrator by way of a first level shifter functioning in use of the electronic circuit to set the quiescent point of the circuit to zero volts at the input of the integrator.
The output of the integrator is preferably coupled to deliver the feedback signal to the voltage-controlled amplifier by way of a second level shifter functioning in use of the electronic circuit as a level set point for the voltage-controlled amplifier.
According to a second aspect of the present invention there is provided a decoding circuit for FM signals comprising in combination an Amplitude Locked Loop and a Phase Locked Loop to give a "noise-alone" signal which is then subtracted from the output of the Phase Locked Loop to give an output signal.
According to a further aspect of the present invention there are provided a number of applications of Amplitude Locked Loop as hereinafter described.
As is well known, a PLL is a servo loop which is slaved or locked to the frequency of a given carrier and is independent of amplitude. By analogy, the ALL is a servo loop which is slaved or locked to the amplitude of a carrier and is independent of frequency.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein:
FIG. 1 is a block circuit diagram of a conventional phase locked loop (PLL) included for explanation only;
FIG. 2 is a block circuit diagram of an amplitude locked loop (ALL) in accordance with the invention;
FIG. 3 is a waveform diagram of various voltages occurring in use of the ALL circuit of FIG. 2;
FIG. 4 is a modified presentation of the block circuit diagram of the ALL of FIG. 2
FIG. 5 is a schematic block diagram of a conventional FM decoder;
FIGS. 6(a) to 6(g) illustrate waveforms existing in FM decoding;
FIG. 7 is a block diagram of an FM decoder employing an Amplitude Locked Loop;
FIG. 8 i

REFERENCES:
patent: 4890066 (1989-12-01), Straver et al.
Sato et al, "CO-4 IE's For High-Quality Demodulators For 4-Channel Discs" IEEE Transactions on Consumer Electronics, vol. CE-21, No. 3, Aug. 1975, pp. 195-202.

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