Demodulator for consumer uses

A demodulator responsive to symbols having a symbol rate in an analog baseband signal comprising analog-to-digital converter means responsive to the signal for sampling the signal only once per symbol to derive a digital output, and digital signal processing circuitry responsive to the digital output of the converter means, the digital processing circuitry being responsive to indications of a function of the digital output derived by the converter means for deriving a digital change indicating signal used in adjusting the relative timing of when the baseband signal is to be sampled by the converter means, and means responsive to the digital change indicating signal to adjust the relative timing for supplying sampling pulses for the baseband signal to the converter means.

A demodulator responsive to symbols having a symbol rate in an analog baseband signal comprising analog-to-digital converter means responsive to the signal for sampling the signal only once per symbol to derive a digital output, and digital signal processing circuitry responsive to the digital output of the converter means, the baseband signal being derived by combining a wave modulated by a carrier with a local frequency source, the digital processing circuitry responding to the converter means to derive a further signal having a value corrected for differences in frequency and phase of the carrier and local frequency source.

A receiver for a modulated input signal having a carrier frequency .omega..sub.i comprising a local oscillator having a frequency .omega..sub.o nominally equal to .omega..sub.i, means responsive to the input signal and the local oscillator for deriving I and Q channel baseband analog signals nominally phase displaced from each other by 90.degree., the I and Q channel baseband signals representing symbols at a symbol rate including residual components due to frequency and phase errors between the carrier and local oscillator frequencies and phases, first and second analog-to-digital converters for respectively sampling the I and Q channel baseband analog signals at a rate of only once per symbol and for deriving first I and Q channel digital signals having values determined by the values of the sampled I and Q analog signals, derotation means responsive to the first I and Q channel digital signals for deriving second I and Q channel digital signals having values corrected for the frequency and phase errors, means responsive to one of the I and Q channel digital signals for controlling when the analog-to-digital converters sample the I and Q channel baseband signals, and output means responsive to the second I and Q channel digital signals.

A demodulator responsive to symbols of an analog signal including residual components due to frequency and phase errors between a carrier on which the signal is modulated and a local frequency source, comprising means responsive to the analog signal for deriving first I and Q channel digital signals having values determined by sampled amplitudes, including the residual components, of the analog signal, and means responsive to the first I and Q channel digital signals for deriving second I and Q channel digital signals corrected for the frequency and phase errors and a third digital signal having a value representing the frequency and phase errors, the second I and Q channel digital signals being derived by combining the first I and Q channel digital signals and the third digital signal in accordance with a CORDIC function.

A receiver responsive to an input signal including symbols modulated on a carrier frequency comprising a local frequency source having an output with a nominal frequency susceptible to variation from a set value therefor, means for combining the input signal and the output of the local source and for deriving first I and Q channel digital signals having values determined by the modulation and by the frequencies and phases of the carrier and the local source, and means responsive to the first I and Q channel digital signals for deriving second I and Q channel digital signals and a third digital signal having a value determined by the relative frequency and phase of the carrier and the local source, the second I and Q channel digital signals having values that are compensated for the deviation of the local source nominal frequency from the set value therefor, the second I and Q channel digital signals being derived by combining the first I and Q channel digital signals and the third digital signal in accordance with a CORDIC function.

A demodulator responsive to symbols of an analog signal, the symbols having a rate, comprising analog-to-digital converter means responsive to the analog signal for sampling the analog signals at approximately the rate so that the signal is sampled only once per symbol and for deriving first I and Q channel digital signals having values determined by the sampled amplitudes of the analog signal, means responsive to the first I and Q channel digital signals for deriving second I and Q channel digital signals and a third digital signal having a value representing frequency and phase corrections to be made to the first I and Q channel digital signals, the second I and Q channel digital signals having values that are compensated by the value of the third digital signal, and a variable digital phase shifter having a first input responsive to one of the first and second digital signals and a second input responsive to clock pulses having approximately the rate for controlling sampling times by the analog-to-digital converting means of the signal at approximately an integral multiple of the rate so that as the value at the first input of the phase shifter changes the sampling times change.

A receiver for a modulated input signal having a carrier frequency x.sub.i comprising a local oscillator having a frequency x.sub.o nominally equal to x.sub.i ;

• the input signal having phase variations as a function of modulation information;
• means responsive to the input signal and the local oscillator for deriving I and Q channel baseband analog signals nominally phase displaced from each other by 90.degree., the baseband analog signals including symbols having a rate, the I and Q channel baseband signals including residual components due to frequency and phase errors between the carrier and local oscillator frequencies and phases, first and second analog-to-digital converters for respectively sampling the I and Q channel baseband analog signals at a rate of only once per symbol and for deriving first I and Q channel digital signals having values determined by the values of the sampled I and Q analog signals, derotation means responsive to the first I and Q channel digital signals for deriving a digital indication of the phase variations corrected for the frequency and phase errors, means responsive to at least one of the digital signals for controlling when the analog-to-digital converters sample the I and Q channel baseband signals, and output means responsive to the digital indication.

A demodulator responsive to symbols of an analog signal including phase variations as a function of information, the symbols having a rate, comprising analog-to-digital converter means responsive to the analog signal for sampling the analog signal at approximately the rate so that the signal is samples only once per symbol and for deriving first I and Q channel digital signals having values determined by the sampled amplitudes of the analog signal, means responsive to the first I and Q channel digital signals for deriving a digital indication of the phase variations and a third digital signal having a value representing frequency and phase corrections to be made to the first I and Q channel digital signals, the value of the digital indication being compensated by the value of the third digital signal, and a variable digital phase shifter having a first input responsive to one of the digital signals and a second input responsive to clock pulses having approximately the rate for controlling sampling times by the analog-to-digital converting means of the signal at approximately an integral multiple of the rate so that as the value at the first input of the phase shifter changes the sampling times change.