Abstract: An IF mixer circuit in a receiver implemented in integrated circuits employs a pair of doubly balance mixers, one injected with a local oscillator reference signal in phase while the quadrature phase of the reference signal is injected into the second mixer. A phase shift circuit adds another 90.degree. phase shift to the output of the second mixer, and the in-phase and out-of-phase signals are applied to a summing circuit to attenuate unwanted mixer products and reinforce the desired IF signal. The balanced elements of the 90.degree. phase shift circuit employ a transistor with equal emitter and collector resistances, a diode-connected transistor in series with the collector load resistance, and a collector-to-base capacitor, which provide a constant-amplitude phase shift in a unity gain structure independent of current, to produce a precise 90.degree. phase shift. Emitter current is adjustable to compensate for production variation in the absolute value of the fixed resistance, i.e.

Abstract: A Darlington-connected transistor pair is modified by the addition of a third transistor to form a three-terminal composite transistor wideband amplifier the current gain of which is approximately double that of a single transistor.