Abstract: A programmable frequency identifier circuit for identifying the frequency of a contaminated signal including a digital finite impulse response filter, a zero crossing detector, a zero crossing counter, and a frequency range decoder. The filter is a programmable filter for filtering signals of the form: S(n)=S.sub.1 (n)+S.sub.2 (n)=A cos 2.pi.F.sub.1 (n)+B cos 2.pi.F.sub.2 (n) where S.sub.1 (n)=desired signal, S.sub.2 (n)=contamination, F.sub.1 =passband frequency, F.sub.2 =stopband frequency, and A,B=constants. The zero-crossing counter counts the sign changes occuring during a programmably determined frame time. The number of zero crossings occuring during the frame time is a number representing the desired frequency. The frequency range decoder is programmed with a plurality of frequency range boundaries similarly represented by a count that is based upon the programmable frame time.

Abstract: Basic block shift registers are cascaded to form a fully programmable linear feedback shift register. Each of the basic block shift registers comprises a plurality of flip-flops, each of which includes control logic circuits. A polynomial equation is first fed into the linear feedback shift register for setting the respective flip-flops into predetermined logic states, which are used to encode messages to be shifted by the programmable linear feedback shift register. The number of flip-flops in the programmable linear feedback shift register can be varied, in accordance to the polynomial equation. Likewise, the polynomial equation also determines the number of times the programmable linear feedback shift register is to circulate the encoded messages.

Abstract: A digital circuit is disclosed for computing the magnitude of a complex number employing piece-wise linear approximations to achieve precision without the need for iteration. An illustrative implementing circuit employs a first stage for converting the in-phase and quadrature signals to their absolute values. The resultant signals are applied to a selection circuit which selects the maximum and minimum values. The resultant signals are combined with coefficients selected as a function of the operating interval and the resultant products added to yield a signal related to the magnitude of the input complex number.