Digital quadrature transmitter with class-B I/Q cell sharing

Patent metadata

Field	Value
Publication number	US-10200232-B1
Application number	US-201715800634-A
Country	US
Kind code	B1
Filing date	Nov 1, 2017
Priority date	Nov 1, 2017
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

A digital quadrature architecture is presented that employs switched current digital power amplifiers and uses a digital class-B input code profile in combination with non-overlapping LO signals to overcome the low efficiency problems of conventional quadrature architectures. By employing digital class-B signals, the number of I/Q cells is reduced to half and the need for extra processing of the sign bits is eliminated in the transmitters, thereby improving the efficiency.

First claim

What is claimed is:

1. A digital transmitter having a quadrature architecture, comprising:
a signal conditioning circuit configured to receive a pair of baseband signals in a digital form and invert both signals in the pair of baseband signals to generate a second pair of inverted baseband signals, wherein the signal conditioning circuit sets negative values in each signal in the pair of baseband signals to zero and sets negative values in each signal in the second pair of inverted baseband signals to zero; and
a digital-to-analog converter comprised of a plurality of unit cells, each unit cell includes a mixing circuit and a converter circuit and each unit cell is configured to receive the pair of baseband signals and the second pair of inverted baseband signals from the signal conditioning circuit,
wherein the mixing circuit mixes each signal in the pair of baseband signals with one of four different clock signals and mixes each signal in the second pair of inverted baseband signal with one of four different clock signals and combines each of the four mixed signals in time domain to create a driving signal with a digital form, where pulses in each of the four different clock signals do not overlap in time with each other;
wherein the converter circuit is configured to receive the driving signal output by the mixing circuit and generates a signal in an analog form at an output, such that the output in each of the unit cells are coupled together at a common node.

2. The digital transmitter of claim 1 wherein data conveyed by the pair of baseband signals is one of single sideband modulated or quadrature amplitude modulated.

3. The digital transmitter of claim 1 further comprises a clock distribution circuit configured to receive a driving clock signal in a digital form and derive the four different clock signals from the driving clock signal, such that each of the four different clock signals has a twenty-five percent duty cycle and is phase shifted with respect to each of the other three clock signals.

4. The digital transmitter of claim 1 wherein the clock distribution circuit receives two differential clock signals which are phase shifted one hundred eighty degrees from each other and includes two divide-by-2 circuits, such that each divide-by-2 circuits receives one of the two differential clock signals.

5. The digital transmitter of claim 1 wherein the mixing circuit mixes each signal in the pair of baseband signals and in the second pair of inverted baseband signal with one of the four different clock signals using a set of different AND gates and combines each of the four mixed signals in time domain using an OR gate.

6. The digital transmitter of claim 1 wherein the mixing circuit is comprised of four AND gates coupled to an OR gate, such that output from each of the AND gates is input to the OR gate.

7. The digital transmitter of claim 1 wherein the converter circuit is a current source, wherein the current source is controlled by the driving signal output by the mixing circuit and the outputs of the current sources in each of the unit cells are coupled together at a common node.

8. The digital transmitter of claim 7 wherein the current source includes at least one transistor, where a control terminal of the at least one transistor is driven by the driving signal.

9. The digital transmitter of claim 1 further comprises a binary to thermometer decoder interposed between the signal conditioning circuit and the digital-to-analog converter.

10. A digital transmitter, comprising:
a signal conditioning circuit configured to receive a pair of baseband signals in a digital form and invert both signals in the pair of baseband signals to generate a second pair of inverted baseband signals, wherein data conveyed by the pair of baseband signals is one of single sideband modulated or quadrature amplitude modulated, wherein the signal conditioning circuit sets negative values in each signal in the pair of baseband signals to zero and sets negative values in each signal in the second pair of inverted baseband signals to zero;
a clock distribution circuit configured to receive two differential clock signals in a digital form which are phase shifted one hundred eighty degrees from each other and operates to generate four different clock signals from the two differential clock signals, such that each of the four different clock signals has a twenty-five percent duty cycle and is phase shifted with respect to each of the other three clock signals; and
a digital-to-analog converter comprised of a plurality of unit cells, each unit cell includes a mixing circuit and a converter circuit and each unit cell is configured to receive the pair of baseband signals and the second pair of inverted baseband signals from the signal conditioning circuit,
wherein the mixing circuit mixes each signal in the pair of baseband signals with one of four different clock signals and mixes each signal in the second pair of inverted baseband signal with one of the four different clock signals and combines each of the four mixed signals in time domain to create a driving signal with a digital form, where pulses in each of the four different clock signals do not overlap in time with each other;
wherein the converter circuit is configured to receive the driving signal output by the mixing circuit and generates a signal in an analog form at an output, such that the output in each of the unit cells are coupled together at a common node.

11. digital transmitter of claim 10 wherein the mixing circuit mixes each signal in the pair of baseband signals and in the second pair of inverted baseband signal with one of the four different clock signals using a set of AND gates and combines each of the four mixed signals in time domain using an OR gate.

12. The digital transmitter of claim 10 wherein the mixing circuit is comprised of four AND gates coupled to an OR gate, such that output from each of the AND gates is input to the OR gate.

13. The digital transmitter of claim 10 wherein the converter circuit is a current source, wherein the current source is controlled by the driving signal output by the mixing circuit and the outputs of the current sources in each of the unit cells are coupled together at a common node.

14. The digital transmitter of claim 13 wherein the current source includes at least one transistor, where a control terminal of the at least one transistor is driven by the driving signal.

15. The digital transmitter of claim 10 further comprises a binary to thermometer decoder interposed between the signal conditioning circuit and the digital-to-analog converter.

16. The digital transmitter of claim 10 operates in a Multi-Use Radio Service frequency band.

17. The digital transmitter of claim 10 wherein the signal conditioning circuit, the clock distribution circuit and the digital-to-analog converter are implemented on the same integrated circuit.

Assignees

• Univ Michigan Regents

Inventors

• Wentzloff David D
• Kim Hun-Seok
• Kosari Avish

Classifications

• H04L5/22

  using time-division multiplexing · CPC title

• H04B1/04

  Circuits · CPC title

• H04L27/362 Primary

  Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated (H04L27/366 takes precedence) · CPC title

• H04L5/0007

  the frequencies being orthogonal, e.g. OFDM(A) or DMT · CPC title