Digital processing of pilot-tone amplitudes

Apparatus for digitally representing the amplitude of each of at least two pilot tone signals having mutually exclusive frequencies, the at least two signals indicating a relative position of a servo controlled device and being part of an input signal set whose amplitude is represented in an input digital representation, the apparatus comprising:

• a processor responsive to the frequencies of the at least two signals for deriving a digital representation of the sine and cosine functions of the frequency of each of the at least two signals, the processor including:
• a synthesizer for receiving signals at the frequencies of the at least two signals for deriving a digital representation of the frequency of each of the at least two signals;
• and
• a look-up table containing digital representations of a sine and a cosine function for the frequencies of the at least two signals, the look-up table being responsive to the synthesizer to select the digital representation of the sine and cosine functions for each of the at least two signals based on the digital representations of the frequency of each of the at least two signals;
• and
• means responsive to the selected digital representations of the sine and cosine functions for each of the at least two signals and to the input digital representation for deriving a digital representation of the amplitude of each of the at least two signals.

Apparatus for digitally representing the amplitude of each of at least two pilot tone signals having mutually exclusive frequencies, the at least two signals indicating a relative position of a servo controlled device and being part of an input signal set whose amplitude is represented in an input digital representation, the apparatus comprising:

• a synthesizer for receiving signals at the frequencies of the at least two signals for deriving a digital representation of the frequency of each of the at least two signals;
• and
• a look-up table containing digital representations of a sine and a cosine function for the frequencies of the at least two signals, the look-up table being responsive to the synthesizer to select the digital representation of the sine and cosine functions for each of the at least two signals based on the digital representations of the frequency of each of the at least two signals;
• and
• a time-shared bi-quadratic filter responsive to the selected digital representations of the sine and cosine functions for each of the at least two signals and to the input digital representation to derive a first digital representation for each of the at least two signals based on the sine function of each of the at least two signals and a second digital representation for each of the at least two signals based on the cosine function of each of the at least two signals, and to derive a digital representation of the amplitude of each of the at least two signals based on the first and second digital representations for each of the at least two signals.

A process for digitally representing amplitudes of first and second pilot tone signals having mutually exclusive frequencies, the amplitudes of the first and second pilot tone signals indicating a relative position of a servo controlled device and being part of an input signals set whose amplitude is represented in an input digital representation, the process comprising:

• deriving a digital representation of a frequency of the first pilot tone signal;
• deriving a digital representation of a frequency of the second pilot tone signal;
• deriving a digital representation of a sine function and a cosine function of the frequency of the first pilot tone signal based on the digital representation of the frequency of the first pilot tone signal;
• deriving a digital representation of a sine function and a cosine function of the frequency of the second pilot tone signal based on the digital representation of the frequency of the second pilot tone signal;
• mixing the digital representation of the sine and cosine functions of the frequency of the first pilot tone signal with the input digital representation to derive a digital representation of a sine component and a cosine component of the first pilot tone signal;
• mixing the digital representation of the sine and cosine functions of the frequency of the second pilot tone signal with the input digital representation to derive a digital representation of a sine component and a cosine component of the second pilot tone signal;
• processing the digital representation of the sine and cosine components of the first pilot tone signal to derive a digital representation of an amplitude of the first pilot tone signal;
• and
• processing the digital representation of the sine and cosine components of the second pilot tone signal to derive a digital representation of an amplitude of the second pilot tone signal.