Coincidence demodulator
A coincidence (Latin: coincidentia = collapse) or phase demodulator is an analog electrical circuit for demodulating frequency-modulated signals. In contrast to discriminators, it directly generates a phase modulation , which is then demodulated immediately.
Layout and function
The main component of the coincidence demodulator is a logical AND or EXOR gate or a multiplier with two inputs. The frequency-modulated signal, which previously went through a limiter amplifier and is therefore square-wave, goes directly to one of its inputs. It reaches the second input with a fixed amount. The time shift is often achieved with an oscillating circuit or a ceramic oscillator, which delays the signal by exactly a quarter period (90 °) of the frequency if there is no modulation (center frequency). A pulse-width modulated signal is produced at the output of the logic gate or multiplier. The desired LF signal is created from this by a low pass or integrator.
A typical example of a coincidence demodulator is the integrated circuit of the TBA120 type, which contains a coincidence demodulator with a multiplier and the limiter amplifier. It requires a precisely matched external oscillating circuit or ceramic oscillator for phase shifting.
At the time of tube technology , the EQ80 tube that was specially developed by Philips was used. The variant was mainly used in some devices from Philips, but ultimately could not prevail over the ratio detector .
literature
- Martin Gerhard Wegener: Modern radio reception technology. Franzis-Verlag, Munich 1985, ISBN 3-7723-7911-7 & Yüce-Group, Istanbul 1989, ISBN 975-411-058-1
- Expertise in radio, television and information electronics. Europa-Verlag 2000, ISBN 3-8085-3284-X