Frequency Selective Logarithmic Amplifier With Intrinsic Frequency Demodulation Capability

摘要

A regenerative selective logarithmic detector amplifier (LDA) can have integrated FM demodulation capabilities. It can receive a wired or wireless FM modulated signal and amplify or demodulate it with high sensitivity, high skirt ratio and minimized noise when compared to the prior art. When used in conjunction with other circuits such as a PLL or mixer, it can improve interference rejection and frequency selectivity and be locked on a precise channel in frequency and phase. The LDA produces intermittent oscillations that are self-quenched when reaching a given threshold. It also embeds the circuitry to perform direct FM discrimination. FM demodulation process is completed by a simple analog or digital frequency to voltage converter. This plus the fact that the instantaneous regeneration gain is low-medium permit to detect signals of small amplitudes buried in the noise.

主权项

1. A system for use in a receive chain of a communication device, the system comprising:
an amplifying circuit configured to receive an input signal and to generate an oscillation based on the input signal; one or more quadripole resonant circuits configured to establish a frequency pass band transfer response with a substantially zero phase region, the one or more quadripole resonant circuits coupled to the amplifying circuit and configured to establish a frequency of operation of the system; a sampling circuit coupled to the amplifying circuit and configured to terminate the oscillation based on a predetermined threshold so as to periodically clamp and restart the oscillation to generate a series of voltage spikes, wherein an instantaneous frequency of the voltage spikes carries frequency modulation (FM) and amplitude modulation (AM) modulation information of the input signal and is output as a output signal, and wherein the output signal has a different frequency than the input signal; and a low pass filter circuit coupled between the amplifier circuit and the sampling circuit to isolate the output signal from the input signal and the oscillation generated by the amplifier.