Non-linear function generating circuit and method

A method for processing an input signal, comprising the steps of:

• (a) modulating an input signal using a sigma-delta modulator to produce a modulated input signal;
• (b) performing a non-linear function upon the modulated input signal to produce a feedback signal, the feedback signal being a non-linear function of the modulated input signal, the feedback signal being distinct from the input signal;
• and
• (c) feeding back the feedback signal to the sigma-delta modulator.

Apparatus for producing a signal representative of the square root of an input signal, such apparatus, comprising:

• a feedback loop having:
• a sigma-delta modulator fed by the input signal and a feedback signal, the output of the sigma-delta modulator is a stream of m-bit digital words;
• a filter for converting the stream of m-bit digital words produced by the sigma-delta modulator into a corresponding stream of n-bit digital words;
• a multiplier fed by the n-bit and m-bit streams of digital words, the multiplier producing a series of digital words, each one of the digital words representing the product of one of the n-bit digital words and a one of the n-bit digital words, the series of digital words produced by the multiplier being fed to the sigma-delta modulator as the feedback signal.

Apparatus for processing an input signal, comprising:

• a feedback loop having:
• a sigma-delta modulator fed by the input signal and a feedback signal, the output of the sigma-delta modulator is a stream of m-bit digital words;
• a filter for converting the stream of m-bit digital words produced by the sigma-delta modulator into a corresponding stream of n-bit digital words;
• a non-linear processing unit fed by the n-bit and m-bit streams of digital words, the non-linear processing unit producing a series of digital words, each one of the digital words representing a non-linear combination of one of the n-bit digital words and one of the n-bit digital words, the series of digital words produced by the non-linear processor being fed to the sigma-delta modulator as the feedback signal.

Apparatus for producing a signal representative of the square root of an input signal, such apparatus, comprising:

• a feedback loop comprising:
• a modulator having:
• a differencing network for producing a signal representative of the difference between the input signal and a feed back signal;
• an integrator fed by the difference signal;
• and comparator fed by the integrator, for producing a series of bits representative of the difference between the input signal and the feedback signal;
• a decimation filter fed by the series of bits for converting the sets of the series of bits into a corresponding sequence of n bit digital words;
• and
• a multiplier fed by the series of bits and the sequence of n bits digital words for producing the feedback signal.