Tuned phase stable limiter amplifier

DETAILED DESCRIPTION The foregoing objects and other objects are attained wherein there is provided in accordance with the invention a limiter amplifier comprising a pair of bipolar transistors arranged in a common emitter, balanced push-pull amplifier type of configuration with their emitters coupled together through a tuning capacitor.
The capacitance value of the tuning capacitor is selected so as to series resonate with the inductive components of the emitter source impedances of the two bipolar transistors in a particular frequency band.
A constant current source is connected to the emitter of each transistor.
Capacitively coupling the emitters of the transistors in accordance with the invention and using constant current sources in each emitter circuit results in a differential amplifier type of configuration for the particular frequency band.
By using the capacitor to resonate out the inherent inductance of the emitters of the transistors in the particular frequency band, increased gain of the limiter amplifier is obtained.
Also, because the emitters are capacitively coupled, the limiter amplifier acts as a series resonant bandpass filter rejecting signals of frequencies outside the band.
Selecting the value of the capacitor to result in resonance at the center frequency of the particular frequency pass band results in a limiter amplifier which amplifies, limits and filters.
By configuring the transistors in a balanced push-pull configuration in accordance with the invention, there is very low even order nonlinearity and a phase stable limiter amplifier results for input signals of large dynamic range.
Because of the use of the limiting/amplifying transistors to perform a bandpass filtering function in accordance with the invention, external bandpass filters may not by required between gain stages.
Additionally, a limiter amplifier in accordance with the invention is particularly suitable for construction in a monolithic semiconductor substrate and hybrid assembly.