Synchronous demodulator employing a common-base transistor amplifier

Claim 1

In a detector for recovering the information content of a modulated input signal and of the type including a switching section formed from two transistors having a pair of base electrodes biased to a predetermined potential level by one terminal of a first source of energizing potential and between which reference carrier switching signals are applied, a pair of collector electrodes to provide demodulated output signals representative of said information content and at which a direct voltage output of the detector is developed, and a pair of emitter electrodes commonly coupled to receive an intermediate signal corresponding to said modulated input signal from the collector electrode of an included amplifier transistor to which said input signal is applied, the improvement comprising: means interconnecting the base and emitter electrodes of said amplifier transistor in a common base circuit configuration with a source supplying said modulated input signals and with a second source of energizing potential of lesser voltage value than thaT of said first source of energizing potential to inhibit such forward biasing of the base-collector junction of said amplifier transistor by said input signals as would cause reverse biasing of the base-emitter junction of both of said switching transistors and an undesirable shift in the direct voltage output of said detector; said means including: a. a first resistance means coupling a first terminal of said source of modulated input signals to the emitter electrode of said amplifier transistor for applying input signals thereto; b. direct current means coupling a first terminal of said second source of energizing potential to the base electrode of said amplifier transistor and maintaining a substantially fixed potential thereon; c. direct current means coupling a second terminal of said source of modulated input signals, a second terminal of said first source of energizing potential, and a second terminal of said second source of energizing potential to a circuit junction point; and d. means coupling said junction point to a point of reference potential such that input signals are applied to said amplifier transistor between its emitter and base electrodes, output signals are developed by said transistor between its collector and base electrodes for coupling to said switching section transistor emitter electrodes, and the potential at the collector electrode of said amplifier transistor is effectively clamped with respect to said reference potential with supplied input signals of increasing magnitudes at substantially the voltage value of said second source of energizing potential.