Study and Investigation Of MOSFET IC FM Discriminator

Abstract

The detection of an FM signal should be linear over a sufficiently wide frequency range, and insensitive to amplitude variations of the incoming FM signal. There are several FM demodulators used to demodulate FM signals, namely:

the Slope detector, the Foster-Seely · discriminator, the ratio detector, Quadrature detector, and PLL demodulator. In this work we present a novel circuit that can be used as an FM discriminator. The pmposed FM detector consists of two loops:

The active loop which is sensitive to the FM signal to be demodulated, and the compensation loop, which is sensitive to the local oscillator frequency.

The first loop is constructed of:

Frequency Controlled Current Source (FCCS), and NMOSFET differential Amplifier.

The second loop is consists of:

Frequency Controlled Current Source (FCCS), and NMOSFET differential Amplifier.

The first and second loops are both monitored by a difference amplifier to cancel out the common mode signals from the main and compensation loops. This circuit is based on the frequency controlled current source (FCCS).

In this circuit, the average output voltage varies fairly linearly with varying frequency. When the frequency increases the average value of the output voltage increases. The proposed circuit functions as a frequency detector which is fairly linear over wide range of frequencies. Conventional FM discriminators can not be fully integrated because of the large capacitors and inductors involved in their implementation. In this thesis a development of a fully integrated FM discriminator is achieved. The overall system can be implemented in a single chip using VLSI technology.