IP2 CALIBRATION MEASUREMENT AND SIGNAL GENERATION

• US 20110275341A1
• Filed: 05/10/2010
• Published: 11/10/2011
• Est. Priority Date: 05/10/2010
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Dubash, Noshir, Babitch, Daniel, Landmark, Joakim
• Granted Patent: US 8,634,793 B2
• Time in Patent Office: Days
• US Class Current: 455/318
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A radio frequency receiver on an integrated circuit (RFIC) includes an oscillator circuit, which generates a radio frequency (RF) oscillatory signal having a predetermined frequency that is outside of an intermediate frequency passband of the RFIC. An amplitude modulator modulates the RF oscillatory signal to produce an amplitude modulated signal which is applied to a mixer that downconverts the amplitude modulated signal. A calibration circuit receives the downconverted signal, including second order modulation (IM2) products, and, responsive to the IM2 products, generates a bias signal that is applied to the mixer to reduce the IM2 products.

Claims

1. A radio frequency receiver on an integrated circuit (RFIC), the RFIC comprising:

a source of radio frequency (RF) signals configured in a first mode to provide received RF signals and in a second mode to provide a predetermined amplitude modulated (AM) RF signals;

a local oscillator configured to provide a local oscillatory signal;

a mixer coupled to the source of RF signals and to the local oscillator for downconverting the RF signals to produce intermediate frequency (IF) signals having frequencies within an IF passband;

a calibration circuit coupled to the mixer, the calibration circuit configured to receive the IF signal from the mixer when the source of RF signals in in the second mode, to detect second order modulation (IM2) products in the IF signal, to generate a bias signal, to apply the bias signal to the mixer and to adjust the bias signal in a sense determined by the detected IM2 products to reduce the IM2 products;

2. The RFIC according to claim 1, wherein the source of RF signals includes an RF amplifier configured to be coupled to an antenna to provide the RF signals when the source of RF signals is in the first mode and a source of AM RF signals to provide the predetermined AM RF signals when the source of RF signals is in the second mode, wherein the predetermined AM RF signals have a frequency outside of the IF passband.

3. The RFIC according to claim 2, wherein the source of AM RF signals includes an oscillatory circuit which produces oscillatory RF signals and, and wherein the source of RF signals further includes an RF filter circuit which is configured to filter the RF signals provided by the RF amplifier when the source of RF signals is in the first mode and is configured as a resonant circuit of the oscillatory circuit when the source of RF signals is in the second mode.

4. The RFIC according to claim 3, wherein the source of AM RF signals further includes an amplitude modulator which modulates the RF oscillatory signals produced by the oscillatory circuit with a modulating signal to produce the predetermined AM RF signals.

5. The RFIC according to claim 1, wherein the calibration circuit is configured to measure the IM2 products over a plurality of clock pulses and to select the bias voltage based on the measured IM2 products over the plurality of clock pulses.

6. The RFIC according to claim 1, wherein the mixer includes:

a differential mixer including a plurality of switching devices, and

wherein the plurality of switching devices are configured to receive respective local oscillator (LO) signals, wherein at least one of the LO signals is modified by the bias voltage to reduce the IM2 products.

7. The RFIC according to claim 1, wherein the RFIC includes an RF amplifier, a filter circuit and circuitry which, responsive to a control signal, reconfigures the RF amplifier and the filter circuit as the oscillator circuit.

8. The RFIC according to claim 1, further including control circuitry which controls the oscillator to generate the oscillatory signal in a calibration mode and disables the oscillator in an operational mode.

9. The RFIC according to claim 1, further comprising an IF filter, coupled to the mixer, the IF filter configured to filter the IF signal of the mixer within the IF passband to provide a filtered IF output signal to the calibration circuit;

10. The RFIC according to claim 9, wherein the calibration circuit comprises:

an analog to digital converter configured to digitize the output signal of the IF filter;

an IM2 detector circuit configured to accumulate the IM2 products during a calibration interval; and

an IM2 compensator circuit, responsive to the accumulated IM2 products to provide the bias signal to the mixer.

11. A method for calibrating a radio frequency receiver on an integrated circuit (RFIC) for second order modulation (IM2) products, the method comprising:

generating a radio frequency (RF) oscillatory signal having a frequency that is outside of an intermediate frequency (IF) passband of the RFIC;

modulating the RF oscillatory signal with a periodic modulating signal to provide an amplitude modulated signal;

mixing the amplitude modulated signal with a local oscillator (LO) signal in a mixer to generate a downconverted signal including a second order modulation (IM2) products;

detecting the IM2 products and

adjusting a bias voltage applied to the mixer in a sense determined by the detected IM2 products to reduce the detected IM2 products.

12. The method according to claim 11, wherein adjusting the bias voltage includes:

measuring the IM2 products from the downconverted signal over a plurality of periods of the modulating signal; and

generating the bias voltage based on the measured IM2 products over the plurality of periods of the modulating signal.

13. The method according to claim 12, wherein:

the downconverted signal includes the IM2 products and direct-current (DC) component signals during first intervals of the modulating signal and the DC component signals to the exclusion of IM2 products during second intervals of the modulating signal which alternate with the first intervals; and

the measuring the IM2 products includes, for each of the clock pulses accumulating values representing the IM2 products and DC component signals during the first intervals and subtracting the DC component signals from the accumulated values during the second intervals to measure the IM2 products.

14. The method according to claim 13, wherein generating the bias voltage includes:

accumulating values of the measured IM2 products over a plurality of the intervals to produce an accumulated value; and

changing the bias voltage in a first sense if the accumulated value has first sense and in a second sense, opposite to the first sense, if the accumulated value has a second sense.

15. The method according to claim 14, further wherein the accumulated values are signed values having respective sign bits and the step of changing the bias voltage includes selecting the sign bit of the measured IM2 products to determine the sense of the accumulated IM2 products.

16. The method according to claim 12, further comprising repeating the measuring of the IM2 products and the generating of the bias voltage.

17. The method according to claim 11, wherein the modulating signal is a square wave signal and the modulator modulates the RF oscillatory signal with a modulation index of 1.

18. The method according to claim 11, the further including:

detecting an operating temperature of the RFIC; and

further adjusting the bias voltage applied to the mixer when the detected operating temperature of the RFIC has changed by an amount greater than a predetermined temperature.

19. An second order modulation (IM2) calibrator in a radio frequency receiver on a integrated circuit (RFIC) having a mixer, the IM2 calibrator comprising:

a signal generator, coupled to the mixer, configured to generate an amplitude modulated RF oscillatory signal having a predetermined frequency that is outside of an intermediate frequency (IF) passband of the RFIC, the generated RF signal causing the mixer to produce an output signal that is within the IF passband and that includes IM2 products; and

an IM2 calibration circuit, coupled to the mixer, the IM2 calibration circuit including;

an IM2 detector configured to receive the output signal and to detect the IM2 products in the output signal, and

an IM2 compensation adjustor configured to generate a bias voltage applied to the mixer, based on the detected IM2 products.

20. The IM2 calibrator according to claim 19, wherein the signal generator includes:

an oscillator configured to generate the RF oscillatory signal;

a resonant circuit configured to tune the RF signal to the predetermined frequency.

21. The IM2 calibrator according to claim 20, wherein the resonant circuit is an LC tank circuit.

22. The IM2 calibrator according to claim 20, wherein the signal generator further includes an amplitude modulator, coupled to the oscillator and the mixer, the amplitude modulator configured to modulate the generated RF oscillatory signal with a square-wave signal to provide the modulated RF oscillatory signal,

wherein the mixer generates the output signal from the amplitude modulated signal and a local oscillator (LO) signal.

23. The IM2 calibrator according to claim 22, wherein the amplitude modulator includes a switch, responsive to the square wave signal, for enabling the oscillator when the square wave has a first value and disabling the oscillator when the square wave signal has a second value, different from the first value.

24. The IM2 calibrator according to claim 19, further comprising a controller, coupled to the signal generator and the IM2 calibration circuit, configured to control generation of the RF signal and the selection of the bias voltage.

25. The IM2 calibrator according to claim 19, wherein the IM2 detector includes:

an accumulator for accumulating the IM2 products to the exclusion of other direct current (DC) components over a plurality of clock pulses; and

a register for storing a single bit value associated with the accumulated IM2 products for each of the clock pulses.

26. The IM2 calibrator according to claim 25, wherein the IM2 compensation adjustor generates the bias voltage based on respective values of the single bit value bit over the plurality of pulses.