Method and apparatus for polar receiver with digital demodulation
Circuitry and methods are described for digital signal demodulation. In a polar receiver, a modulated radio-frequency input signal is provided to frequency division circuitry, which may include a harmonic injection-locked oscillator (ILO). The phase of the frequency-divided output is measured using a self-triggered time-to-digital converter (TDC), which may be a Vernier TDC. A subtractor subtracts a period offset from the output of the TDC to generate an offset digital time output, and a digital integrator integrates the offset digital time output. The integrated time signal represents the phase of the radio-frequency input signal and can be used to determine a symbol, such as a phase-shift keying (PSK) or quadrature amplitude modulation (QAM) symbol, conveyed by the modulated radio-frequency input signal.
1. A receiver comprising:
a low-noise amplifier (LNA) operative to amplify a received modulated radio-frequency input signal;
frequency division circuitry connected to the LNA and having an input for receiving the amplified modulated radio-frequency input signal and a frequency-divided output for providing a frequency-divided output signal;
a self-triggered time-to-digital converter (TDC) having a trigger input in communication with the frequency-divided output and a digital time output representing a period of the frequency-divided output signal;
a digital subtractor operative to subtract a period offset from the digital time output to generate an offset digital time output;
a digital integrator in communication with the digital subtractor and operative to generate an integrated time signal representing a phase of the radio-frequency input signal.
2. The receiver of claim 1 , wherein the time-to-digital converter (TDC) is a Vernier TDC.
3. The receiver of claim 1 , further comprising a digital multiplier connected between the digital integrator and the digital subtractor.
4. The receiver of claim 1 , wherein the frequency division circuitry includes:
a harmonic injection locked oscillator (ILO) having an input for receiving the amplified radio-frequency signal; and
a limiter operative to limit an amplitude of an output of the harmonic injection locked oscillator.
5. The receiver of claim 4 , wherein the frequency division circuitry further includes a digital frequency divider connected to an output of the limiter.
6. The receiver of claim 1 , further comprising:
an envelope detector operative to determine an amplitude of the modulated radio-frequency input signal; and
coordinate rotation digital computer (CORDIC) logic operative to identify in-phase (I) and quadrature (Q) components of the modulated radio-frequency input signal from the amplitude and phase of the modulated radio-frequency input signal.
7. A receiver comprising:
a harmonic injection-locked oscillator having an input for receiving a modulated radio-frequency input signal and a frequency-divided output for providing a frequency-divided output signal;
a time-to-digital converter (TDC) having a trigger input in communication with the frequency-divided output and a digital time output representing a period of the frequency-divided output signal;
a digital subtractor operative to subtract a period offset from the digital time output to generate an offset digital time output;
a digital integrator in communication with the digital subtractor and operative to generate an integrated time signal representing a phase of the radio-frequency input signal.
8. The receiver of claim 7 , further comprising a limiter operative to limit an amplitude of the frequency-divided output.
9. The receiver of claim 8 , wherein the frequency division circuitry further includes a digital frequency divider connected to an output of the limiter.
10. The receiver of claim 7 , further comprising a low-noise amplifier operative to amplify the modulated radio-frequency input signal provided to the harmonic injection-locked oscillator.
11. The receiver of claim 7 , wherein the time-to-digital converter is a Vernier time-to-digital converter.
12. The receiver of claim 7 , further comprising a digital multiplier connected between the digital integrator and the digital subtractor.
13. A demodulation method comprising:
receiving a modulated radio-frequency input signal;
dividing the frequency of the radio-frequency input signal using a harmonic injection locked oscillator to generate a frequency-divided signal;
providing the frequency-divided signal to a self-triggered time-to-digital converter (TDC) to obtain a digital time output representing a period of the frequency-divided signal;
subtracting a period offset from the digital time output to generate an offset digital time output; and
integrating the offset digital time output to generate an integrated time signal representing the phase of the radio-frequency input signal.
14. The method of claim 13 , wherein dividing the frequency further includes:
limiting an amplitude of an output of the harmonic injection-locked oscillator; and
providing the amplitude-limited output of the harmonic injection-locked oscillator to a digital frequency divider.
15. The method of claim 13 , further comprising scaling the offset digital time output.
16. The method of claim 13 , wherein the self-triggered time-to-digital converter is a Vernier time-to-digital converter.
17. The method of claim 13 , further comprising:
determining an amplitude of the modulated radio-frequency input signal; and
identifying in-phase (I) and quadrature (Q) components of the phase-modulated radio-frequency input signal from the amplitude and phase of the phase-modulated radio-frequency input signal.
18. A receiver comprising:
frequency division circuitry having an input for receiving a modulated radio-frequency input signal and a frequency-divided output for providing a frequency-divided output signal;
a self-triggered time-to-digital converter (TDC) having a trigger input in communication with the frequency-divided output and a digital time output representing a period of the frequency-divided output signal;
a digital subtractor operative to subtract a period offset from the digital time output to generate an offset digital time output;
a digital multiplier connected to the digital subtractor, the digital multiplier being configured to scale the offset digital time output; and,
a digital integrator in communication with the digital multiplier and operative to generate an integrated time signal representing a phase of the radio-frequency input signal.
19. A receiver comprising:
a harmonic injection locked oscillator (ILO) having an input for receiving a modulated radio-frequency input signal and having a frequency-divided output for providing a frequency-divided output signal;
a limiter operative to limit an amplitude of the frequency-divided output signal;
a self-triggered time-to-digital converter (TDC) having a trigger input in communication with the frequency-divided output and a digital time output representing a period of the frequency-divided output signal;
a digital subtractor operative to subtract a period offset from the digital time output to generate an offset digital time output; and
a digital integrator in communication with the digital subtractor and operative to generate an integrated time signal representing a phase of the radio-frequency input signal.
20. The receiver of claim 19 , wherein the frequency division circuitry further includes a digital frequency divider connected to an output of the limiter.
21. A receiver comprising:
frequency division circuitry having an input for receiving a modulated radio-frequency input signal and a frequency-divided output for providing a frequency-divided output signal;
a self-triggered time-to-digital converter (TDC) having a trigger input in communication with the frequency-divided output and a digital time output representing a period of the frequency-divided output signal;
a digital subtractor operative to subtract a period offset from the digital time output to generate an offset digital time output;
a digital integrator in communication with the digital subtractor and operative to generate an integrated time signal representing a phase of the radio-frequency input signal;
an envelope detector operative to determine an amplitude of the modulated radio-frequency input signal; and
coordinate rotation digital computer (CORDIC) logic operative to identify in-phase (I) and quadrature (Q) components of the modulated radio-frequency input signal from the amplitude and phase of the modulated radio-frequency input signal.
22. A demodulation method comprising:
receiving a modulated radio-frequency input signal;
dividing the frequency of the radio-frequency input signal to generate a frequency-divided signal;
providing the frequency-divided signal to a self-triggered time-to-digital converter (TDC) to obtain a digital time output representing a period of the frequency-divided signal;
subtracting a period offset from the digital time output to generate an offset digital time output; and
scaling the offset digital time output;
integrating the scaled offset digital time output to generate an integrated time signal representing the phase of the radio-frequency input signal.