Some circuit design techniques using two cross-coupled, emitter-coupled pairs

A circuit structure having two cross-coupled, emitter-coupled pairs is proposed as a fundamental analog function element for multiplying two electrical input quantities; the input voltage difference and the tail current difference. The simplest form is well-known as "the Gilbert multiplier cell." In this circuit, the tail current difference is the differential output current of an emitter-coupled pair, nearly proportional to the differential input voltage. Therefore, if the tail current difference is the differential output current of a squaring circuit, nearly proportional to the square of the differential input voltage, a squaring multiplier is obtained and ran be used for radio communication applications as a frequency mixer with a local oscillator frequency doubler. If the tail current difference is the differential output current of a multiplier then a tripler, capable of multiplying three electrical input quantities, is obtained. The folded technique, for low voltage operation, and the multi-tanh technique, for input voltage range expansion, are employed.<
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