Local oscillation generator and local oscillation generating method for reducing frequency pulling

Abstract

This invention provides a local oscillator generator and a method for generating a local oscillator. The local oscillator generator includes an oscillator, a frequency divider, first and second mixers, first and second phase shifters, a summing circuit, and an I / Q generator. The frequency divider divides the oscillation signal from the oscillator to generate first and second divided signals. The first and second mixers mix the first and second divided signals based on the oscillation signal to generate first and second mixed signals, respectively. The first and second phase shifters shift the phases of the first and second mixed signals to generate first and second shifted signals, respectively. The summing circuit sums the first and second shifted signals to generate a summed signal, which the I / Q generator uses to generate a local oscillator signal.

Claims

1. A local oscillator generator, comprising: a controllable oscillator for generating a controllable oscillation signal; a frequency divider for dividing the controllable oscillation signal to generate a first frequency-divided signal and a second frequency-divided signal; a first mixer coupled to the controllable oscillator and the frequency divider for mixing the controllable oscillation signal and the first frequency-divided signal to generate a first mixed signal; a second mixer coupled to the controllable oscillator and the frequency divider for mixing the controllable oscillation signal and the second frequency-divided signal to generate a second mixed signal; and a first phase shifter coupled to the first mixer for phase shifting the first mixed signal to generate a first phase-shifted signal. A second phase shifter, coupled to the second mixer, is used to phase-shift the second mixed signal to generate a second shifted signal; a summing circuit, coupled to the first phase shifter and the second phase shifter, is used to sum the first shifted signal and the second shifted signal to generate a summed signal; and a co-phase and quadrature signal generator is used to generate a co-phase path local oscillator signal and a quadrature path local oscillator signal based on the summed signal; wherein the frequency divider is a first frequency divider, the summing circuit is a first summing circuit, the summed signal is a first summed signal, and the local oscillator generator further includes: a second frequency divider, coupled to the first summing circuit, is used to divide the first summed signal to generate a third frequency-divided signal and a fourth frequency-divided signal; A third phase offsetter, coupled to the second frequency divider, is used to phase offset the third frequency-divided signal to generate a third offset signal; a fourth phase offsetter, coupled to the second frequency divider, is used to phase offset the fourth frequency-divided signal to generate a fourth offset signal. A second summing circuit, coupled to the third phase offsetter and the fourth phase offsetter, is used to sum the third offset signal and the fourth offset signal to generate a second summed signal; wherein the in-phase and quadrature signal generator is used to generate the in-phase path local oscillation signal and the quadrature path local oscillation signal based on the second summed signal.

2. The local oscillator as described in claim 1, wherein the first phase shifter has a low-pass frequency response and the second phase shifter has a high-pass frequency response.

3. The local oscillator generator as described in claim 1, wherein: The first phase shifter includes a first resistor and a first capacitor, a first terminal of the first resistor being used to receive the first mixed signal, and a second terminal of the first resistor being coupled to the first capacitor; and the second phase shifter includes a second resistor and a second capacitor, a first terminal of the second capacitor being used to receive the second mixed signal, and a second terminal of the second capacitor being coupled to the second resistor.

4. The local oscillation generator as described in claim 3, wherein the resistance values ​​of the first resistor and the second resistor are both RA, and the capacitance values ​​of the first capacitor and the second capacitor are both CA.

5. The local oscillator generator as described in claim 4, wherein a frequency of the controllable oscillation signal is fVCO, the first frequency divider is a divide-N frequency divider, where N is a positive integer, and (RA × CA) is determined based on (fVCO - (fVCO / N)).

6. The local oscillator generator as described in claim 1, wherein the third phase shifter has a low-pass frequency response and the fourth phase shifter has a high-pass frequency response.

7. The local oscillator generator as described in claim 1, wherein: The third phase shifter includes a third resistor and a third capacitor, a first terminal of the third resistor being used to receive the third frequency-divided signal, and a second terminal of the third resistor being coupled to the third capacitor; and the fourth phase shifter includes a fourth resistor and a fourth capacitor, a first terminal of the fourth capacitor being used to receive the fourth frequency-divided signal, and a second terminal of the fourth capacitor being coupled to the fourth resistor.

8. The local oscillator as described in claim 7, wherein the resistance values ​​of the third resistor and the fourth resistor are both RB, and the capacitance values ​​of the third capacitor and the fourth capacitor are both CB.

9. The local oscillator generator as described in claim 8, wherein a frequency of the controllable oscillation signal is fVCO, the first frequency divider is an N-division frequency divider, the second frequency divider is an M-division frequency divider, N and M are both positive integers, and (RB × CB) is determined based on ((fVCO - (fVCO / N)) / M).

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