Local oscillator leakage detecting and cancellation

Abstract

A mixer circuitry comprises a mixer, a local oscillator (LO) leakage detector, a digital LO leakage cancellation controller and a DAC arrangement. The mixer is configured to mix a first LO signal having an LO frequency fLO with an intermediate frequency (IF) signal and generate an output signal, i.e. a wanted signal. The LO leakage detector measures the LO leakage at the output of the mixer in the presence of the wanted signal. Then in the digital LO leakage cancellation controller, a digital algorithm is run that automatically adjusts the LO leakage in the mixer by steering the digital-to-analog converter arrangement such that the intermediate frequency input signal level to the mixer is adjusted.

1 . A mixer circuitry for detecting and cancelling Local Oscillator (LO) leakage, comprising:
 a first mixer configured to mix a first LO signal having an LO frequency with an Intermediate Frequency (IF) signal and generate a first output signal;   a LO leakage detector configured to receive the first output signal from the first mixer and generate a digital word representing LO leakage detected from the first mixer;   a digital processing unit is configured to process the digital word representing the LO leakage detected from the first mixer and generate a control word; and   a Digital-to-Analog Converter (DAC) arrangement coupled to the IF signal of the first mixer and configured to receive the control word and adjust the IF signal of the first mixer.   
     
     
         2 . The mixer circuitry according to  claim 1 , wherein the LO leakage detector comprises:
 a coupler coupled to an output of the first mixer;   a second mixer configured to mix a second oscillator signal with the first output signal of the first mixer received from the coupler and generate a second output signal;   a third quadrature mixer configured to mix the second output signal of the second mixer with an LO signal having a same frequency as the first LO signal, and generate quadrature output signals having a same frequency as a frequency of the second oscillator signal, via an output;   an amplifier arrangement coupled to the third quadrature mixer for amplifying and filtering the quadrature output signals from the third quadrature mixer, and generating a third output signal;   a fourth mixer arrangement configured to mix the third output signal from the amplifier arrangement with the second oscillator signal and generate a Direct Current (DC) signal; and   an Analog-to-Digital Converter (ADC) arrangement for converting the DC signal from the fourth mixer arrangement and generating the digital word.   
     
     
         3 . The mixer circuitry according to  claim 2 , wherein the frequency of the second oscillator signal is lower than a frequency of the IF signal. 
     
     
         4 . The mixer circuitry according to  claim 2 , wherein the amplifier arrangement comprises two amplifiers for amplifying and filtering the quadrature output signals from the third quadrature mixer in parallel. 
     
     
         5 . The mixer circuitry according to  claim 2 , wherein the fourth mixer arrangement comprises two mixers, and the ADC arrangement comprises two ADCs. 
     
     
         6 . The mixer circuitry according to  claim 2 , wherein the fourth mixer arrangement comprises one single mixer, and the ADC arrangement comprises one single ADC. 
     
     
         7 . The mixer circuitry according to  claim 2  further comprising a selector coupled to the output of the third quadrature mixer for selecting one of the quadrature output signals from the third quadrature mixer at a time, and wherein the amplifier arrangement comprises one single amplifier coupled to the output of the third quadrature mixer via the selector for amplifying and filtering one of the quadrature output signals at a time. 
     
     
         8 . The mixer circuitry according to  claim 1 , wherein the digital processing unit is configured to accumulate the LO leakage over a number of samples to generate the control word to adjust settings of the DAC arrangement such that an average of the LO leakage is minimized. 
     
     
         9 . The mixer circuitry according to  claim 1 , wherein the first mixer is a quadrature mixer, and the DAC arrangement comprises two DACs configured to receive the control word and adjust the IF signal of the first mixer. 
     
     
         10 . The mixer circuitry according to  claim 9 , wherein the digital processing unit is configured to accumulate I-phase and Q-phase LO leakage over a number of samples to generate the control word to adjust settings of the two DACs such that an average of the I-phase and Q-phase LO leakage (I 2 +Q 2 ) is minimized. 
     
     
         11 . The mixer circuitry according to  claim 10 , wherein the coupler is a capacitor. 
     
     
         12 . An electronic circuit comprising mixer circuitry, the mixer circuitry comprising:
 a first mixer configured to mix a first Local Oscillator (LO) signal having an LO frequency with an Intermediate Frequency (IF) signal and generate a first output signal;   a LO leakage detector configured to receive the first output signal from the first mixer and generate a digital word representing the LO leakage detected from the first mixer;   a digital processing unit configured to process the digital word representing LO leakage detected from the first mixer and generate a control word; and   a Digital-to-Analog Converter (DAC) arrangement coupled to the IF signal of the first mixer and receive the control word and adjust the IF signal of the first mixer.   
     
     
         13 . The electronic circuit according to  claim 12 , wherein the LO leakage detector comprises:
 a coupler coupled to an output of the first mixer;   a second mixer configured to mix a second oscillator signal with the first output signal of the first mixer received from the coupler and generate a second output signal;   a third quadrature mixer configured to mix the second output signal of the second mixer with an LO signal having a same frequency as the first LO signal, and generate quadrature output signals having a same frequency as a frequency of the second oscillator signal, via an output;   an amplifier arrangement coupled to the third quadrature mixer for amplifying and filtering the quadrature output signals from the third quadrature mixer, and generating a third output;   a fourth mixer arrangement configured to mix the third output signal from the amplifier arrangement with the second oscillator signal and generate a direct current (DC) signal; and   an analog-to-digital converter (ADC) arrangement for converting the DC signal from the fourth mixer arrangement and generating the digital word.   
     
     
         14 . The electronic circuit according to  claim 12 , wherein the frequency of the second oscillator signal is lower than a frequency of the IF signal. 
     
     
         15 . The electronic circuit according to  claim 13 , wherein the amplifier arrangement comprises two amplifiers for amplifying and filtering the quadrature output signals from the third quadrature mixer in parallel. 
     
     
         16 . The electronic circuit according to  13 , wherein the fourth mixer arrangement comprises two mixers, and the ADC arrangement comprises two ADCs. 
     
     
         17 . The electronic circuit according to  claim 13 , wherein the fourth mixer arrangement comprises one single mixer, and the ADC arrangement comprises one single ADC. 
     
     
         18 . The electronic circuit according to  claim 13  further comprising a selector coupled to the output of the third quadrature mixer for selecting one of the quadrature output signals from the third quadrature mixer at a time, and wherein the amplifier arrangement comprises one single amplifier coupled to the output of the third quadrature mixer via the selector for amplifying and filtering one of the quadrature output signals at a time. 
     
     
         19 . The electronic circuit according to  claim 13  comprising any one of a frequency synthesiser, a transceiver, a transmitter, or a receiver. 
     
     
         20 . The electronic circuit according to  claim 13  comprising any one of a base station, beamforming base station, a mobile terminal, or a user equipment for a cellular communications system or in a wireless communication system.