Calibrated quadrature very low intermediate frequency receiver
View Patent ↗The present invention is a quadrature VLIF receiver, including calibration circuitry, and methods to closely match signal processing of an in-phase signal path and a quadrature-phase signal path to optimize VLIF image rejection. The calibration circuitry includes a variable gain variable-phase calibration signal generator, a variable gain amplifier for each signal path, phase adjustment circuitry for each signal path, and switching circuitry to support calibration steps. The calibration signal generator supplies a calibration signal at the same frequency as mixer local oscillator signals; therefore, during calibration, all signals downstream of the VLIF mixer are at DC, which simplifies calibration measurements, thereby minimizing calibration times.
1. A quadrature very low intermediate frequency (VLIF) receiver comprising:
an in-phase local oscillator circuit adapted to provide an in-phase radio frequency (RF) local oscillator signal;
a quadrature-phase local oscillator circuit adapted to provide a quadrature-phase RF local oscillator signal, wherein the quadrature-phase RF local oscillator signal is phase-shifted essentially 90 degrees from the in-phase RF local oscillator signal;
calibration signal generator circuitry adapted to provide an RF calibration signal during calibration, wherein the in-phase RF local oscillator signal, the quadrature-phase RF local oscillator signal, and the RF calibration signal are at a first calibration frequency;
an in-phase VLIF mixer circuit adapted to receive the in-phase RF local oscillator signal and the RF calibration signal during calibration to generate an in-phase VLIF mixer calibration output signal;
a quadrature-phase VLIF mixer circuit adapted to receive the quadrature-phase RF local oscillator signal and the RF calibration signal during calibration to generate a quadrature-phase VLIF mixer calibration output signal; and
calibration circuitry including an in-phase phase adjustment circuit; and a quadrature-phase phase adjustment circuit, the calibration circuitry adapted to receive during calibration:
the in-phase VLIF mixer calibration output signal to generate at least one in-phase calibration factor, wherein the at least one in-phase calibration factor further comprises an in-phase gain calibration factor and an in-phase phase calibration factor; and
the quadrature-phase VLIF mixer calibration output signal to generate at least one quadrature-phase calibration factor, wherein the at least one quadrature-phase calibration factor further comprises a quadrature-phase gain calibration factor and a quadrature-phase phase calibration factor;
wherein at least one of the in-phase phase adjustment circuit and the quadrature-phase phase adjustment circuit is adjusted based on the in-phase phase calibration factor and the quadrature-phase phase calibration factor;
wherein the in-phase phase adjustment circuit further includes an in-phase summing circuit adapted to receive the in-phase VLIF mixer calibration output signal during calibration and the quadrature-phase VLIF mixer calibration output signal during calibration, and the in-phase phase adjustment circuitry is further adapted to add a portion of the quadrature-phase VLIF mixer calibration output signal to the in-phase VLIF mixer calibration output signal during calibration to generate a calibrated in-phase VLIF calibration output signal;
wherein the quadrature-phase phase adjustment circuit further comprises a quadrature-phase summing circuit adapted to receive the in-phase VLIF mixer calibration output signal during calibration and the quadrature-phase VLIF mixer calibration output signal during calibration; and
wherein the quadrature-phase phase adjustment circuitry is further adapted to add a portion of the in-phase VLIF mixer calibration output signal to the quadrature-phase VLIF mixer calibration output signal during calibration to generate a calibrated quadrature-phase VLIF calibration output signal.
2. The quadrature VLIF receiver of claim 1 , wherein:
the in-phase VLIF mixer circuit is further adapted to receive the in-phase RF local oscillator signal and an RF input signal during normal operation to generate an in-phase VLIF mixer output signal;
the quadrature-phase VLIF mixer circuit is further adapted to receive the quadrature-phase RF local oscillator signal and the RF input signal during normal operation to generate a quadrature-phase VLIF mixer output signal; and
the calibration circuitry is further adapted:
to receive the in-phase VLIF mixer output signal during normal operation;
to receive the quadrature-phase VLIF mixer output signal during normal operation;
to apply the in-phase gain calibration factor and the in-phase phase calibration factor to the in-phase VLIF mixer output signal during normal operation to generate a calibrated in-phase VLIF output signal; and
to apply the quadrature-phase gain calibration factor and the quadrature-phase phase calibration factor to the quadrature-phase VLIF mixer output signal during normal operation to generate a calibrated quadrature-phase VLIF output signal.
3. The quadrature VLIF receiver of claim 2 , wherein:
an amplitude of the calibrated in-phase VLIF output signal is essentially equal to an amplitude of the calibrated quadrature-phase VLIF output signal; and
the calibrated in-phase VLIF output signal is phase-shifted essentially 90 degrees from the calibrated quadrature-phase VLIF output signal.
4. The quadrature VLIF receiver of claim 1 , wherein the calibration circuitry further comprises:
an in-phase variable gain VLIF amplifier;
a quadrature-phase variable gain VLIF amplifier; and
wherein at least one of the in-phase variable gain VLIF amplifier and the quadrature-phase variable gain VLIF amplifier is gain adjusted based on the in-phase gain calibration factor and the quadrature-phase gain calibration factor.
5. The quadrature VLIF receiver of claim 1 , further including a first RF frequency synthesizer circuit configured to generate the in-phase RF local oscillator signal, the quadrature-phase RF local oscillator signal, and the RF calibration signal.
6. The quadrature VLIF receiver of claim 1 , further comprising passive components and switching circuitry, wherein during calibration the passive components are disconnected from other quadrature VLIF receiver circuitry.
7. The quadrature VLIF receiver of claim 1 , wherein the quadrature VLIF receiver is adapted to determine the in-phase phase calibration factor, wherein the quadrature VLIF receiver is configured to adjust a phase of the RF calibration signal,
wherein the RF calibration signal is:
phase-shifted essentially 45 degrees from the in-phase RF local oscillator signal; and
phase-shifted essentially 45 degrees from the quadrature-phase RF local oscillator signal; and
the quadrature VLIF receiver further adapted to measure the amplitude of the in-phase VLIF mixer calibration output signal; and
the quadrature VLIF receiver further adapted to determine the quadrature-phase phase calibration factor, wherein the controller is adapted to adjust a phase of the RF calibration signal wherein the RF calibration signal is:
phase-shifted essentially 45 degrees from the in-phase RF local oscillator signal; and
phase-shifted essentially 45 degrees from the quadrature-phase RF local oscillator signal; and
the quadrature VLIF receiver further adapted to measure the amplitude of the quadrature-phase VLIF mixer calibration output signal.