Digital variable gain mixer

• US 20070072558A1
• Filed: 03/30/2006
• Published: 03/29/2007
• Est. Priority Date: 09/26/2005
• Status: Active Grant

• Current Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Original Assignee: ST Wireless SA
• Inventors: Eshraghi, Aria, Sridharan, Srinath, Welland, David, Emira, Ahmed
• Granted Patent: US 7,697,901 B2
• Time in Patent Office: Days
• US Class Current: 455/86
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence

Abstract

A method includes controlling a mixer gain to provide a range of selected power output levels from the mixer using a first control scheme for a low portion of the range and using a second control scheme for a high portion of the range. Using the selected mixer gain, incoming baseband signals may be upconverted in the mixer to a transmission frequency and output from the mixer at the selected power output level.

Claims

1. A method comprising:

controlling a gain of a mixer to provide a range of selected power output levels from the mixer using a first control scheme for a low portion of the range and using a second control scheme for a high portion of the range; and

upconverting incoming baseband signals in the mixer to a transmission frequency and outputting transmission signals from the mixer at the selected power output level.

2. The method of claim 1, wherein the first control scheme comprises controlling a current density of the incoming baseband signals coupled to one or more mixer slices, and the second control scheme comprises coupling the incoming baseband signals to additional mixer slices at a fixed current density.

3. The method of claim 1, wherein using the first control scheme comprises:

digitally controlling a current density of the incoming baseband signals; and

coupling the controlled incoming baseband signals to at least one of a plurality of mixer slices for mixing with a local oscillator signal.

4. The method of claim 3, further comprising digitally enabling the at least one of the plurality of mixer slices to receive the controlled incoming baseband signals to attain the gain at a selected power output level.

5. The method of claim 1, wherein the second control scheme comprises digitally enabling a selected number of a plurality of mixer slices to receive the incoming baseband signals at a fixed current density level.

6. An apparatus comprising:

a current density controller to receive an incoming baseband signal and to adjust a current density level of the incoming baseband signal under digital control;

a mixer coupled to the current density controller, the mixer including a plurality of slices each capable of receiving the incoming baseband signal at the current density level when enabled, wherein the plurality of slices are individually enabled under the digital control; and

a decoder coupled to receive control information and provide the digital control to the current density controller and the mixer.

7. The apparatus of claim 6, wherein the current density controller comprises a current mirror having a controllable gain to generate a tail current from the incoming baseband signal, the tail current having an adjustable current density level based on the controllable gain.

8. The apparatus of claim 7, wherein each of the plurality of slices includes enable circuitry to disable the slice under the digital control.

9. The apparatus of claim 8, wherein each of the plurality of slices includes a plurality of buffers coupled to receive a local oscillator output, a mixer circuit to modulate the local oscillator output with the tail current, and at least one cascode switch coupled between an output of the mixer circuit and an output of the slice, the cascode switch to disable a path to the output of the slice when the slice is disabled and provide isolation from a transmit output.

10. The apparatus of claim 6, wherein the mixer is to output a radio frequency (RF) signal at a selected power level, wherein the current density controller is to adjust the current density level if the selected power level is in a first range.

11. The apparatus of claim 10, wherein the decoder is to enable at least one of the plurality of slices to receive the incoming baseband signal at a fixed current density level if the selected power level is in a second range, the second range greater than the first range.

12. The apparatus of claim 6, wherein the mixer is to receive an unmodulated carrier signal from a local oscillator and to mix the unmodulated carrier signal with the incoming baseband signal in a first mode of operation, the incoming baseband signal being modulated.

13. The apparatus of claim 12, wherein the mixer is to receive and buffer a modulated signal from the local oscillator and to mix the modulated signal with a DC current in a second mode of operation.

14. The apparatus of claim 6, wherein the current density controller is to vary the current density level in a low range of power output levels and to fix the current density level at a maximum value in a high range of power output levels.

15. A mixer comprising:

a first slice having a first pair of buffers to receive local oscillator (LO) signals of different polarities, a first pair of switches to receive and pass tail currents of different polarities, and a first mixer circuit to mix the LO signals with the tail currents; and

a second slice having a second pair of buffers to receive the LO signals, a second pair of switches to receive and pass the tail currents, and a second mixer circuit to mix the LO signals with the tail currents, wherein the second slice comprises a mirror image of the first slice with respect to a first axis.

16. The mixer of claim 15, further comprising a third slice having a third pair of buffers to receive the LO signals, a third pair of switches to receive and pass the tail currents, and a third mixer circuit to mix the LO signals with the tail currents, wherein the third slice comprises a mirror image of the first slice with respect to a second axis.

17. The mixer of claim 15, wherein the first slice and the second slice comprise an in-phase portion of individual slices of the mixer and a quadrature-phase portion of the individual slices, wherein the quadrature-phase portion is substantially symmetric to the in-phase portion with respect to an axis.

18. The mixer of claim 15, wherein the second slice is to cancel a flux created in the first slice by an incoming LO signal of a first polarity and the first slice is to cancel a flux created in the second slice by an incoming LO signal of a second polarity.

19. The mixer of claim 15, wherein the first slice is to receive the tail currents corresponding to modulated baseband signals to mix with unmodulated LO signals in an 8-PSK mode.

20. The mixer of claim 19, wherein the first slice is to receive the tail currents corresponding to a DC current to mix with modulated LO signals in a GMSK mode.

21. The mixer of claim 15, wherein the first pair of switches and the second pair of switches are proximally located with respect to the first axis and the first pair of buffers and the second pair of buffers are distally located with respect to the first axis.

22. The mixer of claim 21, wherein the first mixer circuit is located between the first pair of switches and the first pair of buffers with respect to the first axis.

23. A system comprising:

a transceiver having an interface to receive baseband data from a processor, the transceiver including a mixer to mix the baseband data with a radio frequency (RF) signal to provide an RF output, wherein the mixer is digitally controlled to provide the RF output with a variable gain;

a power amplifier coupled to the transceiver to receive the RF output; and

an antenna coupled to the power amplifier to transmit and receive information.

24. The system of claim 23, wherein the transceiver further comprises a decoder to enable at least one of a first plurality of slices of the mixer to receive baseband data at a variable current density level if the variable gain is in a first range and to enable at least one of a second plurality of slices to receive the baseband data at a fixed current density level if the variable gain is in a second range, the second range greater than the first range.

25. The system of claim 23, wherein the transceiver further comprises a current density controller to vary a current density level of the baseband data in a low range of the variable gain and to fix the current density level at a maximum value in a high range of the variable gain.

26. The system of claim 23, wherein the mixer includes a first plurality of slices having input components and mixer components arranged according to a first layout and a second plurality of slices having input components and mixer components arranged according to a second layout, the second layout comprising a mirror image of the first layout, wherein the first plurality of slices cancel a flux created in the second plurality of slices by an incoming local oscillator signal of a first polarity and the second plurality of slices cancel a flux created in the first plurality of slices by an incoming local oscillator signal of a second polarity.