Adaptive/configurable intermediate frequency (IF) wireless receiver and bluetooth device using the same

1. A wireless receiver having a normal signal receiving mode, the wireless receiver comprising:

a low noise amplifier amplifying an input RF signal;

an adjustable local radio frequency (RF) synthesizer providing a local RF clock signal with a variable frequency;

a RF mixer down-converting the amplified RF signal to an analog intermediate frequency (IF) signal by mixing the local RF clock signal with the amplified RF signal;

a filter filtering the analog IF signal;

an analog-to-digital converter (ADC) converting the filtered analog IF signal to a digital IF signal;

an adjustable digital local IF synthesizer providing a digital local IF clock signal with a variable frequency;

a digital mixer down-converting the digital IF signal to a baseband signal by mixing the digital local IF clock signal with the digital IF signal;

an IF configuration unit configuring the adjustable local RF synthesizer to vary the frequency of the local RF clock signal, and configuring the adjustable digital local IF synthesizer to vary the frequency of the digital local IF clock signal; and

a signal detection and IF calculation unit measuring a direct current (DC) offset, a second order inter-modulation (IM2) component and/or a flicker noise in the baseband signal, and determining or adjusting a nominal frequency of the analog IF signal adaptively based on measured values of the DC offset, the IM2 component and/or the flicker noise until a minimum nominal frequency of the analog IF signal is obtained such that measured values of the DC offset, the IM2 and the flicker noise satisfy a requirement for correct demodulation, wherein the IF configuration unit is caused to configure the adjustable local RF synthesizer and the adjustable digital local IF synthesizer based on the nominal frequency of the analog IF signal determined by the signal detection and IF calculation unit to ensure that the RF mixer obtains the analog IF signal with the nominal frequency and the digital mixer obtains the normal baseband signal of the normal signal receiving mode, wherein the signal detection and IF calculation unit performs operations of:

comparing the measured values of the DC offset, the IM2 component and/or the flicker noise with corresponding thresholds;

decreasing the nominal frequency of the analog IF signal in a predetermined step when all of the measured values are less than the corresponding thresholds; and

obtaining the minimum nominal frequency of the analog IF signal so that all of the measured values are less than the corresponding thresholds.

2. The wireless receiver according to claim 1 , wherein when the wireless receiver is powered up or reset, the signal detection and IF calculation unit is caused to measure the DC offset, the IM2 component and/or the flicker noise in the baseband signal, and determine or adjust the nominal frequency of the analog IF signal adaptively based on the measured values of the DC offset, the IM2 component and/or the flicker noise.

3. The wireless receiver according to claim 1 , wherein in the normal signal receiving mode, the signal detection and IF calculation unit is caused to analyze the baseband signal to obtain a frequency offset between a local RF clock signal in a TX path of a wireless transmitter and the local RF clock signal in a RX path of the wireless receiver, and determine or adjust the nominal frequency of the analog IF signal adaptively based on the frequency offset, and the IF configuration unit configures the adjustable digital local IF synthesizer to vary the frequency of the digital local IF clock signal to compensate the frequency offset.

4. The wireless receiver according to claim 1 , wherein the wireless receiver has a TX DC offset self calibration mode, and the wireless receiver and a wireless transmitter on a same device form a RF transceiver, wherein

in the TX DC offset self calibration mode, the wireless receiver receives the RF signal transmitted by the wireless transmitter, the wireless receiver and the RF transmitter share a common local RF clock signal, and the IF configuration unit causes the adjustable local RF synthesizer to provide the common local RF clock signal to ensure that the RF mixer obtains the analog IF signal with 0 frequency and turns on a switch connected with the digital mixer in parallel to output the digital IF signal with 0 frequency from the analog to digital converter directly.

5. The wireless receiver according to claim 1 , wherein the wireless receiver has a fast channel scan mode, and a receiving bandwidth of the wireless receiver in the fast channel scan mode is wider than that in the normal signal receiving mode, and wherein the IF configuration unit causes the adjustable local RF synthesizer and the adjustable digital local IF synthesizer to support the fast channel scan mode.

6. The wireless receiver according to claim 1 , wherein the wireless receiver is a narrow band communication system, and the analog IF signal is an ultra low range.

7. The wireless receiver according to claim 1 , wherein the adjustable local RF synthesizer comprises a phase frequency detector, a loop filter, a voltage controlled oscillator, an adjustable fractional divider, a buffer and a quadrature clock generator; and wherein

the phase frequency detector detects a phase difference between a local reference frequency signal and a signal generated by the fractional divider and outputs an error voltage according to the phase difference;

the loop filter filters the error voltage;

the voltage controlled oscillator outputs a local clock signal according to the filtered error voltage;

the fractional divider divides the clock signal outputted from the voltage controlled oscillator according to a division factor thereof;

the buffer buffers the local clock signal;

the quadrature clock generator generates a first local clock signal and a second local clock signal having the same frequency and 90 degree phase difference with the first local clock signal according to the local clock signal;

the IF configuration unit causes the adjustable local RF synthesizer to vary the frequency of the local RF clock signal by varying the division factor, and

the first local clock signal and the second local clock signal serve as the local RF clock signal.

8. A Bluetooth device having a normal signal receiving mode, the Bluetooth device comprising:

a RF transmitter;

a wireless receiver comprising:

a low noise amplifier amplifying an input RF signal;

an adjustable local radio frequency (RF) synthesizer providing a local RF clock signal with a variable frequency;

a RF mixer down-converting the amplified RF signal to an analog intermediate frequency (IF) signal by mixing the local RF clock signal with the amplified RF signal;

a filter filtering the analog IF signal;

an analog-to-digital converter (ADC) converting the filtered analog IF signal to a digital IF signal;

an adjustable digital local IF synthesizer providing a digital local IF clock signal with a variable frequency;

a digital mixer down-converting the digital IF signal to a baseband signal by mixing the digital local IF clock signal with the digital IF signal; and

an IF configuration unit configuring the adjustable local RF synthesizer to vary the frequency of the local RF clock signal, and configuring the adjustable digital local IF synthesizer to vary the frequency of the digital local IF clock signal; and

a signal detection and IF calculation unit measuring a direct current (DC) offset, a second order inter-modulation (IM2) component and/or a flicker noise in the baseband signal, and determining or adjusting a nominal frequency of the analog IF signal adaptively based on measured values of the DC offset, the IM2 component and/or the flicker noise until a minimum nominal frequency of the analog IF signal is obtained such that measured values of the DC offset, the IM2 and the flicker noise satisfy a requirement for correct demodulation, wherein the IF configuration unit is caused to configure the adjustable local RF synthesizer and the adjustable digital local IF synthesizer based on the nominal frequency of the analog IF signal determined by the signal detection and IF calculation unit to ensure that the RF mixer obtains the analog IF signal with the nominal frequency and the digital mixer obtains the normal baseband signal of the normal signal receiving mode, wherein the signal detection and IF calculation unit performs operations of:

comparing the measured values of the DC offset, the IM2 component and/or the flicker noise with corresponding thresholds;

decreasing the nominal frequency of the analog IF signal in a predetermined step when all of the measured values are less than the corresponding thresholds; and

obtaining the minimum nominal frequency of the analog IF signal so that all of the measured values are less than the corresponding thresholds.

9. The Bluetooth device according to claim 8 , wherein when the wireless receiver is powered up or reset, the signal detection and IF calculation unit is caused to measure the DC offset, the IM2 component and/or the flicker noise in the baseband signal, and determine or adjust the nominal frequency of the analog IF signal adaptively based on the measured values of the DC offset, the IM2 component and/or the flicker noise.

10. The Bluetooth device according to claim 8 , wherein in the normal signal receiving mode, the signal detection and IF calculation unit is caused to analyze the baseband signal to obtain a frequency offset between a local RF clock signal in a TX path of a wireless transmitter and the local RF clock signal in a RX path of the wireless receiver, and determine or adjust the nominal frequency of the analog IF signal adaptively based on the frequency offset, and the IF configuration unit configures the adjustable digital local IF synthesizer to vary the frequency of the digital local IF clock signal to compensate the frequency offset.

11. The Bluetooth device according to claim 8 , wherein the wireless receiver has a TX DC offset self calibration mode, and the wireless receiver and a wireless transmitter on the same device form a RF transceiver, and wherein

in the TX DC offset self calibration mode, the wireless receiver receives the RF signal transmitted by the wireless transmitter, the wireless receiver and the RF transmitter share a common local RF clock signal, and the IF configuration unit causes the adjustable local RF synthesizer to provide the common local RF clock signal to ensure that the RF mixer obtains the analog IF signal with 0 frequency and turns on a switch connected with the digital mixer in parallel to output the digital IF signal with 0 frequency from the analog to digital converter directly.

12. The Bluetooth device according to claim 8 , wherein the wireless receiver has a fast channel scan mode, and a receiving bandwidth of the wireless receiver in the fast channel scan mode is wider than that in the normal signal receiving mode, and wherein the IF configuration unit causes the adjustable local RF synthesizer and the adjustable digital local IF synthesizer to support the fast channel scan mode.

13. The Bluetooth device according to claim 8 , wherein the wireless receiver is a narrow band communication system, and the analog IF signal is an ultra low range.