Multi-function passive frequency mixer
View Patent ↗A frequency-mixing device performing voltage multiplying and low-pass filtering operations in addition to frequency mixing is provided. The three operations may be carried out with the same components by designing the frequency mixer appropriately. The frequency mixer comprises a first capacitance connected in series to the input of the frequency-mixing device, a first switch connected in parallel to the first capacitance, a second switch connected in series to the first capacitance, and a second capacitance connected in parallel to the second switching means. The switches are controlled by a local oscillator signal to close and open alternately according to a change in the voltage level of the first oscillator signal.
1. A frequency-mixing device comprising:
a first input port for a local oscillator signal having a frequency adapted to mix an input signal of the frequency-mixing device to a desired frequency;
a second input port for the input signal to be frequency-mixed;
a first capacitance operationally coupled in series between the second input port and an output port of the frequency-mixing device;
a first switch operationally coupled between the first capacitance and a ground level;
a second switch operationally coupled in series to the first capacitance, and
a second capacitance operationally coupled between the second switch and the ground level,
wherein the first switch and the second switch are configured to close and open alternately in response to a change in the voltage level of the oscillator signal.
2. The device of claim 1 , wherein the local oscillator signal is the first local oscillator signal, the device further comprising an input port for a second local oscillator signal having the same frequency as the first local oscillator signal and a substantially opposite phase, and wherein the first switch is configured to close and open in response to the first local oscillator signal and the second switch is configured to close and open in response to the second local oscillator signal.
3. The device of claim 2 , wherein the switches are implemented with NMOS transistors.
4. The device of claim 1 , wherein the mixing device is configured to function also as a voltage multiplier by adapting the oscillator signal to close the first switch and accordingly charge the first capacitance during the first half cycle of the first local oscillator signal, and by adapting the second oscillator signal to close the second switch and accordingly release the charge in the first capacitance together with the input signal to the second capacitance during the second half cycle of the second local oscillator signal.
5. The device of claim 1 , wherein the mixing device also functions as a low-pass filter having a corner frequency defined by the ratio of the first capacitance and the second capacitance.
6. The device of claim 1 , wherein the output port of the frequency mixing-device is connected between the second switch and the second capacitance.
7. The device of claim 1 , wherein the mixing device is configured to convert a radio frequency input signal to a baseband or to an intermediate frequency.
8. The device of claim 1 , wherein one of the first switch and the second switch is implemented with an NMOS transistor and the other is implemented with a PMOS transistor.
9. The device of claim 1 , further comprising two balanced input ports and output ports, a third capacitance connected in series to one input port, and a third switch, wherein the first capacitance is connected in series to the other input port, the third switch is connected in series to the third capacitance, and the second capacitance is connected between the second switch and the third switch.
10. The device of claim 1 , wherein the first switch is implemented with two transistors with gates and sources connected to each other, and a drain of at least one of the transistors connected to the first capacitance.
11. The device of claim 1 , wherein a direct current voltage source is connected to the substrates of the transistors.
12. A frequency-mixing device comprising:
a first input port for a local oscillator signal having a frequency adapted to mix an input signal of the frequency-mixing device to a desired frequency;
a balanced input port for an input signal to be frequency-mixed, the balanced input port comprising a first input and a second input;
a balanced output port for a frequency-mixed output signal, the balanced output port comprising a first output and a second output;
a first capacitance operationally coupled in series between the first input of the balanced input port and the first output of the balanced output port;
a second capacitance operationally coupled in series between the first input of the balanced input port and the first output of the balanced output port;
a first switch operationally coupled between the first capacitance and the second capacitance;
a second switch operationally coupled in series to the first capacitance;
a third switch operationally coupled in series to the second capacitance, and
a third capacitance operationally coupled between the second switch and the third switch,
wherein the first switch is configured to close and open alternately with the second switch and the third switch in response to a change in the voltage level of the oscillator signal.
13. A frequency-mixing method in a frequency-mixing device, the method comprising:
producing an oscillator signal having a frequency adapted to mix an input signal of the frequency-mixing device to a desired frequency;
charging a first capacitance connected in series to an input port of the frequency-mixing device with an input signal sample during the first half cycle of the oscillator signal; and
charging a second capacitance operationally coupled to the first capacitance with the charge in the first capacitance together with the input signal during the second half cycle of the oscillator signal.
14. The method of claim 13 , wherein the first capacitance and the second capacitance are charged alternately.
15. The method of claim 13 , wherein the local oscillator signal is the first local oscillator signal, the method further comprising:
producing a second local oscillator signal having the same frequency as the first local oscillator signal and a substantially opposite phase;
charging the first capacitance during the first half cycle of the first oscillator signal;
charging the second capacitance during the second half cycle of the second oscillator signal.
16. The method of claim 13 , further comprising low-pass filtering the frequency mixed signal by defining a low-pass corner frequency with the ratio of the first capacitance and the second capacitance.
17. The method of claim 13 , further comprising obtaining a frequency-mixed output signal from between the first capacitance and the second capacitance.
18. A radio transceiver comprising a local oscillator and a frequency-mixing device, wherein the local oscillator is configured to produce a local oscillator signal to be input to the frequency-mixing device or to produce a signal to be used in forming the local oscillator signal, the frequency-mixing device comprising:
a first input port for the local oscillator signal having a frequency adapted to mix an input signal of the frequency mixing device to a desired frequency;
a second input port for the input signal to be frequency-mixed;
a first capacitance operationally coupled in series between the second input port and an output port of the frequency mixing device;
a first switch operationally coupled between the first capacitance and a ground level;
a second switch operationally coupled in series to the first capacitance, and
a second capacitance operationally coupled between the second switch and the ground level,
wherein the first switch and the second switch are configured to close and open alternately in response to a change in the voltage level of the oscillator signal.
19. The radio transceiver of claim 18 , wherein the local oscillator signal is the first local oscillator signal, the frequency-mixing device further comprising an input port for a second local oscillator signal having the same frequency as the first local oscillator signal and a substantially opposite phase, and wherein the first switch is configured to close and open in response to the first local oscillator signal, and the second switch is configured to close and open in response to the second local oscillator signal.
20. The radio transceiver of claim 19 , wherein the radio transceiver is configured to receive a radio frequency signal comprising an in-phase component and a quadrature component, and the radio transceiver comprises a separate frequency mixer for the in-phase component and the quadrature component.
21. The radio transceiver of claim 20 , wherein the phases of the local oscillator signal applied to the frequency mixer associated with the quadrature component differ 90 degrees from the respective phases of the local oscillator signals applied to the frequency mixer associated with the in-phase component, and the local oscillator signals have a pulse ratio of 25/75 at most.
22. The radio transceiver of claim 20 , further comprising a separate amplifier for each frequency mixer to precede the frequency mixers, and wherein the phases of the local oscillator signals applied to the frequency mixer associated with the quadrature component differ 90 degrees from the respective phases of the local oscillator signals applied to the frequency mixer associated with the in-phase component and the local oscillator signals have a pulse ratio of 50/50 at most.
23. The radio transceiver of claim 20 , further comprising a phase shifter preceding at least one of the frequency mixers, and the phase shifter preceding at least one of the frequency mixers shifting the phase of at least one of the in-phase component and the quadrature component to produce a 90-degree phase difference between the in-phase component and the quadrature component.
24. The radio transceiver of claim 23 , wherein the same local oscillator signals are applied to both frequency mixers.
25. The radio transceiver of claim 18 , wherein the radio transceiver is a mobile communication device.
26. A frequency-mixing device comprising:
a local oscillator providing a local oscillator signal having a frequency adapted to mix an input signal of the frequency-mixing device to a desired frequency;
a first capacitance operationally coupled in series between an input port and an output port of the frequency-mixing device;
a first switch operationally coupled between the first capacitance and a ground level;
a second switch operationally coupled in series to the first capacitance, and
a second capacitance operationally coupled between the second switch and the ground level,
wherein the first switch and the second switch are configured to close and open alternately in response to a change in the voltage level of the oscillator signal.
27. A frequency-mixing device comprising:
means for obtaining an oscillator signal having a frequency adapted to mix an input signal of the frequency-mixing device to a desired frequency;
means for charging a first capacitance connected in series to an input port of the frequency-mixing device with an input signal sample during the first half cycle of the oscillator signal, and
means for charging a second capacitance operationally coupled to the first capacitance with the charge in the first capacitance together with the input signal during the second half cycle of the oscillator signal.