Quadrature demodulator and wireless receiver

A quadrature demodulator includes a quadrature demodulating circuit configured to generate an analog in-phase signal and an analog quadrature signal based on an output signal of a low noise amplifier, and a controller configured to cause a thermal noise, instead of the output signal of the low noise amplifier, to be input to the quadrature demodulating circuit, when a correction parameter to correct a mismatch between the in-phase and quadrature signals is being calibrated.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-177761, filed Sep. 9, 2015, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a quadrature demodulator and a wireless receiver.

BACKGROUND

In the related art, there is a wireless receiver having a quadrature demodulator. A wireless receiver of one such type has a function of correcting a phase difference between an in-phase component and a quadrature component of a wireless signal (hereinafter, referred to as “IQ mismatch”), so that accuracy of received data is improved.

The IQ mismatch represents a gain error and a phase error between an I-channel signal and a Q-channel signal. This IQ mismatch is caused by inaccuracies in a 90° phase shifter in the quadrature demodulator and difference in path length between the I channel and the Q channel.

A method to correct the IQ mismatch would be to calculate a correction amount of the IQ mismatch using a phase shift circuit in a loop back circuit from the transmission side to the reception side. However, since this method requires the phase shift circuit, the total size of the wireless receiver would become larger and manufacturing cost thereof would be increased.

Another method to correct the IG mismatch would be using a thermal noise which is included in an output from a low noise amplifier. This method can improve correction accuracy of the IQ mismatch without enlarging the total size of the wireless receiver.

However, according to the method that uses thermal noise, when a disturbance wave signal such as a reception signal is generated and contained in the thermal noise, it may not be possible to detect the IQ mismatch. That is, during the reception of the disturbance wave signal, the IQ mismatch may not be correctable. For this reason, a correction parameter of the IQ mismatch has to be calculated after confirming that there is no disturbance wave signal. In other words, it is not possible to correct the IQ mismatch while the disturbance wave signal is being generated.

DETAILED DESCRIPTION

Here, one or more example embodiments provide a quadrature demodulator and a wireless receiver which can detect IQ mismatch based on a thermal noise signal regardless of generation of a disturbance wave signal.

In general, according to an embodiment, a quadrature demodulator includes a quadrature demodulating circuit configured to generate an analog in-phase signal and an analog quadrature signal based on an output signal of a low noise amplifier, and a controller configured to cause a thermal noise, instead of the output signal of the low noise amplifier, to be input to the quadrature demodulating circuit, when a correction parameter to correct a mismatch between the in-phase and quadrature signals is being calibrated.

Hereinafter, embodiments are described with reference to the drawings.

First Embodiment

FIG. 1is a schematic block diagram illustrating a configuration of a quadrature modulator or demodulator according to the example embodiment.

A quadrature modulator and demodulator1is provided in a wireless communication apparatus100which corresponds to a wireless receiver and a wireless transmitter, and includes an antenna2, a low noise amplifier (hereinafter, referred to as a LNA)3, mixers4and5, a phase shifter6, analog-digital converters (hereinafter, referred to as an ADC)7and8, an amplifier9, a variable gain amplifier (hereinafter, referred to as a VGA)10, mixers11and12, a phase shifter13, digital-analog converters (hereinafter, referred to as a DAC)14and15, an oscillator16, a switch17, a control unit18, an antenna switching switch19, a correction unit20, a correction control unit21, a demodulation unit22, and a modulation unit23.

The antenna2is connected to the antenna switching switch19that switches a transmission state into a receiving state.

The antenna switching switch19is controlled by the control unit18, and is connected to the LNA3and the amplifier9.

The LNA3is a circuit that amplifies an output signal of the antenna2with low noise. The output signal of the LNA3is connected to an input terminal of the mixer4and an input terminal of the mixer5via a signal line L1.

The phase shifter6is connected to the mixers4and5. The circuit which includes the mixers4and5, and the phase shifter6is a quadrature demodulating unit.

The phase shifter6is connected to an oscillator16which is a local oscillator. The local signal from the oscillator16is input to the phase shifter6, and the phase shifter6outputs signals which have phases mutually shifted by 90 degrees to the mixers4and5.

Each of outputs of the mixers4and5is connected to each of input terminals of the ADCs7and8.

The mixer4generates an analog signal (hereinafter, referred to as an analog I signal Ai) of an in-phase component by multiplying the output signal of the LNA3by a local signal, and outputs the generated analog signal to the ADC7, and the ADC7outputs a digital signal (hereinafter, referred to as a digital I signal Di) of the in-phase component.

The mixer5generates an analog signal (hereinafter, referred to as an analog Q signal Aq) of a quadrature component by multiplying a local signal by the output signal the LNA3, and outputs the generated analog signal to the ADC8, and the ADC8outputs a digital signal (hereinafter, referred to as a digital Q signal Dq) to the quadrature component.

That is, the quadrature demodulating unit, which includes the mixers4and5, and the phase shifter6, demodulates the output signal of the low noise amplifier3, and generates the analog I signal of the in-phase component and the analog Q signal of the quadrature component. In addition, the ADC7converts the analog I signal into the digital I signal of the in-phase component, and ADC8converts the analog Q signal into the digital Q signal of the quadrature component.

The digital I signal Di and the digital Q signal Dq are input to the correction unit20and the correction control unit21. The correction control unit21calculates, for example, an amount of IQ amplitude mismatch and an amount of IQ phase mismatch by an arithmetic expression which is disclosed in Japanese Patent No. 5,361,927 and then outputs a correction parameter Cp including the amount of IQ amplitude mismatch and the amount of IQ phase mismatch to the correction unit20. An operation of the correction control unit21is controlled by a correction control signal CNT from the control unit18. That is, as disclosed in Japanese patent No. 5,361,927, the correction control unit21configures a correction parameter generation unit which calculates and generates a correction parameter based on the digital I signal and the digital Q signal.

The correction unit20performs the IQ mismatch correcting calculation with the correction parameter Cp. The correction unit20corrects the IQ mismatch between the digital I signal Di and the digital Q signal Dq, and then provides the corrected I signal Dia and the corrected Q signal Dqa to the demodulation unit22.

That is, as disclosed in Japanese Patent No. 5,361,927, the correction unit20performs a primary conversion calculation with the correction parameter Cp, corrects the IQ mismatch between the digital I signal and the digital Q signal, and then generates the correction I signal Dia and the correction Q signal Dqa.

The demodulation unit22generates a demodulation signal based on the input correction I signal Dia and correction Q signal Dqa.

As described, in the reception mode, the wireless signal which is received by the antenna2is amplified by the LNA3, and an analog I signal Ai and an analog Q signal Aq are generated by the mixers4and5. Each of the analog I signal Ai and the analog Q signal Aq is converted into the digital I signal Di and the digital Q signal Dq by the ADCs7and8. The digital I signal Di and the digital Q signal Dq which are output from the ADCs7and8are input to the correction control unit21such that the correction parameter Cp is calculated. The correction unit20performs the correction of the IQ mismatch with respect to the digital I signal Di and the digital Q signal Dq based on the correction parameter Cp, and then the corrected signals are outputs to the demodulation unit22, thereby generating the demodulation signal.

The modulation unit23generates the digital I signal Di of the in-phase component and the digital Q signal Dq of the quadrature component based on input transmitted data rows, and then supplies the generated digital I signal Di of the in-phase component and the digital Q signal Dq of the quadrature component to each of input terminals of the DACs14and15.

Each of the outputs of the DACs14and15is connected to the input terminal of the mixer11and the input terminal of the mixer12. Each of the DACs14and15generates the analog I signal Ai and the analog Q signal Aq, and outputs the generated analog I signal Ai and the analog Q signal Aq to the input terminal of the mixer11and the input terminal of the mixer12.

The phase shifter13is connected to the mixers11and12. The circuit including the mixers11and12, and the phase shifter13is a quadrature modulator.

The phase shifter13is connected to the oscillator16. The local signal is input to the phase shifter13from the oscillator16, and the phase shifter13outputs signals which have phases mutually shifted by 90 degrees to the mixers11and12.

The outputs of the mixers11and12are connected to the input terminal of the VGA10. The mixer11outputs the signal obtained by multiplying the transmission signal from the DAC14to the VGA10by the local signal. The mixer12outputs the signal obtained by multiplying the transmission signal from the DAC15to the VGA10by the local signal.

The gain of the VGA10can be controlled by the control unit18, and the output of the VGA10is connected to the amplifier9. The output of the amplifier9is connected to the antenna switching switch19via a signal line L2.

As described, the amplifier9and the VGA10are connected to the mixers11and12of the quadrature modulator, and are amplifiers for amplifying the outputs of the mixers11and12.

In transmission mode, the transmission signal is generated in the modulation unit23, and is converted into the analog I signal Ai and the analog Q signal Aq in the DACs14and15. The analog I signal Ai and the analog Q signal Aq are quadrature-modulated by the mixers11and12, amplified by the VGA10or the like, and then transmitted from the antenna2.

The switch17is provided on a signal line L3which connects the signal line L1between the LNA3and the mixers4and5, and the signal line L2between the amplifier9and the antenna switching switch19. The switch17is normally in an off state, but when detecting the IQ mismatch, the switch17is turned on, that is, placed in a conductive state by a control signal CS1from the control unit18.

The switch17is controlled to be opened and closed by the control signal CS1from the control unit18. That is, the switch17is a switch that provides the output of the amplifier9to the mixers4and5of the quadrature demodulating unit.

In addition, it is possible to turn off the LNA3by a control signal CS2from the control unit18. For example, the control unit18outputs the control signal CS2, turns off a switch that controls the power supply to the circuit of the LNA3, and thereby turns off the LNA3, which stops its operation. In addition, if the control unit18does not output the control signal CS2, the LNA3is turned on by turning on the switch that controls the power supply to the circuit of the LNA3.

Similarly, it is possible to turn off the quadrature modulating unit by turning off mixers11and12, and the phase shifter13by a control signal CS3from the control unit18. For example, the control unit18outputs the control signal CS3, turns off a switch for controlling the power supply to the circuit of the mixers11and12, and the phase shifter13. Thereby, it is possible to turn off the mixers11and12, and the phase shifter13, which stops its operation. In addition, if the control unit18does not output the control signal CS3, the mixers11and12, and the phase shifter13are turned on by turning on the switch for controlling the power supply to the circuit of the mixers11and12, and the phase shifter13.

When the mixers11and12, and the phase shifter13are turned off, the VGA10amplifies the thermal noise and outputs the thermal noise signal to the amplifier9. That is, the thermal noise signal is included in an output signal output from the amplifier9in a case where the quadrature modulator, which includes the mixers11and12and the phase shifter13, does not perform a modulating operation.

The control unit18controls the entire wireless communication apparatus100including the quadrature demodulator1.

Accordingly, under the control of the control unit18, the quadrature modulator and demodulator1controls the antenna switching switch19such that the transmission and reception are performed by the wireless signal. When detecting the IQ mismatch, under the control of the control unit18, the quadrature modulator and demodulator1outputs the above-described control signals CS1, CS2, and CS3to the switch17, the LNA3, and the mixers11and12, and the phase shifter13, and generates and outputs a correction control signal CNT that controls the operation of the correction control unit21.

Next, a detecting operation of the IQ mismatch based on the thermal noise signal in the quadrature modulator or demodulator1is described.

The control unit18performs a detecting process of the IQ mismatch during a correction time interval. The correction time interval may be a time when it is determined that the wireless communication apparatus100does not perform the transmission and reception, a time during a test mode, or the like.

When the wireless communication apparatus100operates during the correction time interval, the control unit18outputs the control signals CS1, CS2, and CS3to the quadrature modulation unit which includes the switch17, the LNA3, and the mixers11and12, and the phase shifter13.

As a result, the switch17is turned on by the control signal CS1, the LNA3is turned off by the control signal CS2, and the quadrature modulation unit, which includes the mixers11and12, and the phase shifter13, is also turned off by the control signal CS3.

That is, the control unit18outputs the control signal CS2so as to control the LNA3not to perform the amplifying operation when detecting the IQ mismatch, and outputs the control signal CS3. Thereby, the quadrature modulator including the mixers11and12, and the phase shifter13is controlled not to perform the modulation operation. Further, when detecting the IQ mismatch between the analog I signal of the in-phase component and the analog Q signal of the quadrature component, the control unit18performs switching control of the switch17such that the output of the amplifier9is input to the mixers4and5which configure the quadrature demodulating unit, and then controls in such a manner that instead of the output signal of the low noise amplifier3, the thermal noise signal is applied to the mixers4and5.

The LNA3is turned off, and thus a reception signal which is a disturbance wave signal is not input to the mixers4and5. Therefore, at the time of detecting the IQ mismatch, the disturbance wave is not input to the mixers4and5.

In addition, the mixers11and12, and the phase shifter13are turned off, and the quadrature modulator for the transmitting operation is not operated, and thus a load of the oscillator16matches the load on the oscillator encountered in the receiving state. That is, the mixers11and12, and the phase shifter13are turned off, and thus are not affected by a modulation circuit for the transmitting operation. Thereby, it is possible to detect and correct the IQ mismatch with the same load as the load when the mixers11and12, and the phase shifter13are operated by only the demodulation circuit for the reception operation.

Since the mixers11and12, and the phase shifter13are turned off, the signals output from the VGA10and the amplifier9are the thermal noise signals. The control unit18controls the gain of the VGA10so as to make the thermal noise signal to in addition, predetermined size.

The thermal noise signal is supplied to the mixers4and5from the amplifier9via a switch17. The analog I signal Ai and the analog Q signal Aq which are output from the mixers4and5are converted into the digital I signal Di and the digital Q signal Dq by the ADCs7and8and then input to the correction control unit21, so as to calculate the correction parameter Cp. The correction unit20performs the correction of the IQ mismatch with respect to the digital I signal Di and the digital Q signal Dq based on the correction parameter Cp, and then the correction I signal Dia and correction Q signal Dqa in which the IQ mismatch is corrected are output to the demodulation unit22.

Thus, according to the embodiment, it is possible to provide the quadrature demodulator and the wireless receiver which can detect the IQ mismatch based on the thermal noise signal regardless of whether or not a disturbance wave signal is present.

Second Embodiment

In the first embodiment, in order to detect the IQ mismatch of the quadrature demodulator, the output of the quadrature modulator is used as the thermal noise source. However, in the second embodiment, a thermal noise source which is independent of the quadrature modulator is used.

In addition, in second embodiment, the same elements as the quadrature modulator or demodulator1in the first embodiment are denoted by the same reference numerals and only the description for different configurations is given.

FIG. 2is a schematic block diagram illustrating a configuration of the quadrature modulator or demodulator according to the second embodiment. As illustrated inFIG. 2, a quadrature modulator or demodulator1A which is included in a wireless communication apparatus100includes a thermal noise source31.

Thermal noise source31is a circuit that includes a diode, a resistor, and the like, and outputs a thermal noise signal by inputting a predetermined current into the diode or the like.

A switch32is provided on a signal line L1, and the thermal noise source31and the switch32are connected to each other via an amplifier33. Therefore, the thermal noise signal which is output from the thermal noise source31is amplified to be a predetermined size by the amplifier33. Note that, in a case where an output level of the thermal noise signal which is output from the thermal noise source31is sufficiently large, the amplifier33is not necessarily used.

The switch32is a switch that selectively switches inputs to the mixers4and5which configure the quadrature demodulating unit output of the LNA3to any one of outputs of the amplifier33.

The switch32is controlled to be opened and closed by a control signal CS11from a control unit18A. When the control signal CS11is not received, the switch32has a first state in which the output of the LNA3is supplied to the mixers4and5, and when the control signal CS11is received, the switch32has a second state in which the output of the amplifier33is supplied to the mixers4and5.

That is, the control unit18A controls the switch32to be switched such that the thermal noise source31or the output of the amplifier33is input to the mixers4and5by the control signal CS11when detecting the IQ mismatch.

Next, in the quadrature modulator and demodulator1A, detecting operation of the IQ mismatch based on the thermal noise signal is described. The control unit18A operates during a correction interval which is the same as the timing of the detecting process for the IQ mismatch described in first embodiment. The correction interval may be a time when it is determined that the wireless communication apparatus100does not perform the transmission and reception or a time during a test mode.

The control unit18outputs the control signal CS11to the switch32at a predetermined timing.

The switch32enters the second state in which the amplified thermal noise signal, that is, the output of the amplifier33is supplied to the mixers4and5by the control signal CS11. When detecting IQ mismatch, the output from the LNA3is not supplied to the mixers4and5, and a reception signal which is the disturbance wave signal is not input to the mixers4and5.

The thermal noise signal is supplied to the mixers4and5from the switch32. The analog I signal Ai and the analog Q signal Aq which are output from the mixers4and5are respectively converted into the digital I signal Di and the digital Q signal Dq with the ADCs7and8, and input to the correction control unit21to calculate a correction parameter Cp. The correction unit20performs the correction of the IQ mismatch with respect to the digital I signal Di and the digital Q signal Dq based on the correction parameter Cp. Then, the correction I signal Dia and correction of signal Dqa in which the IQ mismatch has been corrected are output to the demodulation unit22.

Therefore, according to the embodiment, it is possible to provide the quadrature demodulator and the wireless receiver which can detect the IQ mismatch based on the thermal noise signal whether or not the disturbance wave signal is present.

Note that, in the above, described two embodiments, the correction interval for performing the detecting process of the IQ mismatch may be the time when the wireless communication apparatus does not perform the transmission and reception or the time during the test mode. However, in a case of a transceiver using a multiple-input and multiple-output (MIMO) technique of corresponding to a plurality of antennas, when an antenna for reception is in a non-use state among the plurality of antennas, only on the antenna for receiving in the non-use state may be subjected to the described detecting process of the IQ mismatch.