Abstract:
Methods and apparatus for demodulating time modulated carriers employ four matched transistors grouped in two comparator pairs. A single constant current source is provided for all four transistors. Emitters of the four transistors are metallically interconnected with each other and with an output of the single constant current source, whereby one of the transistors switches off the other transistors without the use of a capacitive element between transistor pairs. A common threshold reference voltage is applied to one transistor in one comparator pair and to one transistor in the other comparator pair. First and second repetitive pulses, preferably in the form of negative-going ramps, are generated in response to alternate successive zero crossings of the time modulated carrier. The other transistor in the one comparator pair is controlled with the first pulses and the other transistor in the other comparator pair with the second pulses to generate a train of constant area pulses corresponding to zero crossings of the time modulated carrier. The information in the modulated carrier is reproduced by averaging constant area pulses in that train.