MIXER WITH HIGH OUTPUT POWER ACCURACY AND LOW LOCAL OSCILLATOR LEAKAGE

• US 20090075689A1
• Filed: 09/14/2007
• Published: 03/19/2009
• Est. Priority Date: 09/14/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sahota, Gurkanwal Singh, Sun, Bo, Jayaraman, Arun, Aniruddhan, Sankaran
• Granted Patent: US 7,941,115 B2
• Time in Patent Office: Days
• US Class Current: 455/550.100
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H04B 1/0483 Transmitters with multiple parallel paths
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control
• CPC Class Codes: H04B 2001/0491 with frequency synthesizers, frequency converters or modulators

Abstract

A circuit receives a first signal (for example, a baseband signal) and mixes it with a local oscillator (LO) signal, and outputs a second signal (for example, an RFOUT signal). The circuit includes multiple identical Mixer and Frequency Divider Pair (MFDP) circuits. Each MFDP can be enabled separately. Each MFDP includes a mixer and a frequency divider that provides the mixer with a local version of the LO signal. The MFDP outputs are coupled together so that the output power of the second signal (RFOUT) is the combined output powers of the various MFDPs. By controlling the number of enabled MFDPs, the output power of the second signal is controlled. Because the MFDPs all have identical layouts, accuracy of output power step size is improved. Because LO signal power within the circuit automatically changes in proportion to the number of enabled MFDPs, local oscillator leakage problems are avoided.

Claims

1. A circuit comprising:

a plurality of mixer and frequency divider pairs (MFDP), wherein each MFDP can be enabled and disabled separately of each other MFDP, wherein the frequency divider of each MFDP supplies a local oscillator signal to the mixer of the MFDP if the MFDP is enabled, wherein the frequency divider of each MFDP does not supply a local oscillator signal to the mixer of the MFDP if the MFDP is disabled, wherein each MFDP has an output lead, and wherein the output leads of all the MFDPs are coupled together; and

a frequency synthesizer adapted to supply a drive signal to the frequency divider of each of the MFDPs.

2. The circuit of claim 1, wherein each MFDP has a first output lead and a second output lead, wherein the first output leads of all the MFDPs are connected together, and wherein the second output leads of all the MFDPs are connected together.

3. The circuit of claim 1, further comprising:

an amplifier, wherein the output leads of the MFDPs are coupled to an input lead of the amplifier through a transformer.

4. The circuit of claim 1, further comprising:

a baseband filter that receives a baseband signal and outputs a plurality of substantially identical versions of the baseband signal, wherein each version of the baseband signal is supplied to the mixer of a corresponding respective one of the MFDPs.

5. The circuit of claim 4, further comprising:

an amplifier, wherein the plurality of MFDPs supplies an input signal to the amplifier, wherein the input signal has a power, and wherein the power of the input signal is adjusted by enabling and disabling selected ones of the plurality of MFDPs.

6. The circuit of claim 5, wherein the frequency divider of each MFDP outputs a local oscillator signal with an output power if said each MFDP is enabled, wherein the sum of all the output powers of all the local oscillator signals has a magnitude, wherein the ratio of the magnitude of the sum of all the local oscillator output powers to the power of the input signal is substantially constant regardless of how many MFDPs are enabled.

7. The circuit of claim 1, wherein each of the MFDPs has a layout, and wherein the layouts of all the MFDPs are substantially identical.

8. The circuit of claim 1, wherein each MFDP has an associated enable input conductor, wherein a first digital logic value on the enable input conductor enables both the mixer and the frequency divider of the MFDP, and wherein a second digital logic value on the enable input conductor disables both the mixer and the frequency divider of the MFDP.

9. The circuit of claim 1, wherein the frequency divider of each MFDP supplies a local oscillator signal with an output power if said MFDP is enabled, wherein the sum of all the output powers of all the local oscillator signals changes in proportion to the number of MFDPs that are enabled.

10. A circuit comprising:

a frequency synthesizer that outputs a drive signal;

a first frequency divider that receives the drive signal from the frequency synthesizer, the first frequency divider outputting a first local oscillator signal if the first frequency divider is enabled;

a first mixer coupled to receive the first local oscillator signal from the first frequency divider, wherein if the first frequency divider is enabled then the first mixer is enabled and if the first frequency divider is disabled then the first mixer is disabled;

a second frequency divider that receives the drive signal from the frequency synthesizer, the second frequency divider outputting a second local oscillator signal if the second frequency divider is enabled;

a second mixer coupled to receive the second local oscillator signal from the second frequency divider, wherein if the second frequency divider is enabled then the second mixer is enabled and if the second frequency divider is disabled then the second mixer is disabled;

a third frequency divider that receives the drive signal from the frequency synthesizer, the third frequency divider outputting a third local oscillator signal if the third frequency divider is enabled;

a third mixer coupled to receive the third local oscillator signal from the third frequency divider, wherein if the third frequency divider is enabled then the third mixer is enabled and if the third frequency divider is disabled then the third mixer is disabled; and

a driver amplifier, wherein the first, second and third mixers together supply an input signal to the driver amplifier, and wherein the first, second and third mixers can be enabled and disabled independently of one another to change a power with which the input signal drives the driver amplifier.

11. The circuit of claim 10, wherein the circuit has more than three mixers and has more than three frequency dividers, and wherein the circuit is embodied in a cellular telephone.

12. The circuit of claim 11, wherein the first mixer, second mixer, and third mixer have substantially identical layouts, wherein the first frequency divider, the second frequency divider, and the third frequency divider have substantially identical layouts, and wherein the first, second and third mixers and the first, second and third frequency dividers are realized on a single integrated circuit.

13. The circuit of claim 10, wherein the first, second and third local oscillator signals have a combined power, and wherein the ratio of the power with which the input signal drives the driver amplifier to the combined power is substantially constant regardless of how many of the first, second, and third mixers are enabled.

14. A method comprising:

driving an input of an amplifier using one or more of a plurality of mixer and frequency divider pairs (MFDPs), wherein each MFDP has a substantially identical layout, and wherein each MFDP can be enabled or disabled independently of an enabling or disabling of the other MFDPs;

using a frequency synthesizer to supply a drive signal onto an input of the frequency divider of each of the MFDPs; and

changing the number of the MFPDs that are enabled and thereby changing a power with which the plurality of MFDPs drives the input of the amplifier.

15. The method of claim 14, wherein the local oscillators of the plurality of MFDPs generate local oscillator signals having a combined power, and wherein the ratio of the power with which the plurality of MFDPs drives the input of the amplifier to the combined power is substantially constant regardless of how many MFDPs are enabled.

16. The method of claim 14, wherein the MFDPs drive the input of the amplifier through a transformer.

17. The method of claim 14, wherein the ratio of local oscillator leakage power to the power with which the plurality of MFDPs drives the input of the amplifier is substantially constant regardless of how many MFDPs are enabled.

18. A radio transmitter circuit comprising:

a baseband filter;

an amplifier taken from the group consisting of;

a driver amplifier, and a power amplifier; and

means for receiving a baseband signal from the baseband filter and for driving the amplifier, wherein the means can be controlled to change an output power with which the means drives the amplifier, wherein a local oscillator leakage signal at the input of the amplifier has a power, and wherein the ratio of the output power to the power of the local oscillator leakage signal is substantially constant as the output power changes.

19. The radio transmitter circuit of claim 18, wherein the means changes the output power from one of a plurality of discrete output power levels to another selected one of the discrete output power levels, wherein there are at least eight of said discrete output power levels with which the means can be controlled to drive the amplifier.

20. The radio transmitter circuit of claim 19, wherein the means includes a plurality of mixer and frequency divider pairs (MFDPs), wherein each of the MFDPs has a substantially identical layout, and wherein each of the MFDPs can be enabled and disabled independently of the other MFDPs.

21. The radio transmitter circuit of claim 20, wherein each MFDP includes a frequency divider, wherein the means further comprises a frequency synthesizer, and wherein a drive signal output by the frequency synthesizer is supplied to the frequency divider of each of the MFDPs.

22. The radio transmitter circuit of claim 18, wherein the baseband filter, the amplifier, and the means are disposed on a single integrated circuit, and wherein the integrated circuit is a part of a cellular telephone.