# US 8,542,769 B2 · High output power digital TX

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- Number: US 8,542,769 B2
- Document ID: US8542769B2
- Status: Granted
- Kind: B2
- Application number: 13/156,751
- Filed: 2011-06-09
- Published: 2012-12-13
- Granted: 2013-09-24
- Earliest claimed: 2011-06-09
- Assignees: ST-Ericsson SA
- Applicants: Sami Vilhonen
- Inventors: Sami Vilhonen
- Web page: https://patentgrep.com/patent/US8542769B2

## CPC

- H03F 3/45179: {using MOSFET transistors as the active amplifying circuit (H03F3/45278 takes precedence)}
- H03F 3/2175: {using analogue-digital or digital-analogue conversion (H03F3/2173 takes precedence)}
- H03F 3/245: {with semiconductor devices only}
- H03M 1/804: {with charge redistribution}
- H03F 2200/336: A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit
- H03F 2200/537: A transformer being used as coupling element between two amplifying stages
- H03F 2200/541: Transformer coupled at the output of an amplifier
- H04B 2001/0491: {with frequency synthesizers, frequency converters or modulators}
- H03F: AMPLIFIERS
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)
- H04B: TRANSMISSION

## Abstract

The disclosed apparatus and corresponding method uses amplifiers and a differential combiner to control the output power of a digital-to-analog upconverter and to isolate In-phase and Quadrature branches of the upconverter. First and second upconverters convert In-phase and Quadrature portions of a baseband digital value to respective first/second In-phase (Ip/In) and first/second Quadrature (Qp/Qn) analog components at RF. First and second amplifiers respectively amplify Ip, In and Qp, Qn to respectively generate amplified Ip, In and Qp, Qn signals. The first and second amplifiers each operate at a 50% duty cycle and in an interleaved fashion such that only one amplifier is active to generate an output at any time, and such that the amplified signals are output in an interleaved fashion. A differential combiner combines the amplified signals to generate the RF analog signal representative of the baseband digital value.

## Claims

### Claim 1

A digital-to-analog upconverter configured to convert a baseband digital value to a radio frequency (RF) analog signal, said digital-to-analog upconverter comprising:
a first balanced upconverter configured to convert an In-phase portion of the baseband digital value to a first In-phase analog component (Ip) at a radio frequency and a second In-phase analog component (In) at the radio frequency, where In is phase-shifted relative to Ip;
a second balanced upconverter configured to convert a Quadrature portion of the baseband digital value to a first Quadrature analog component (Qp) at the radio frequency and a second Quadrature analog component (Qn) at the radio frequency, where Qp is phase-shifted relative to Qn;
a first amplifier configured to amplify Ip and In to generate amplified Ip and In signals at first and second In-phase amplifier outputs;
a second amplifier configured to amplify Qp and Qn to generate amplified Qp and Qn signals at first and second Quadrature amplifier outputs;
wherein the first and second amplifiers each operate at a 50% duty cycle and in an interleaved fashion such that only one of the first and second amplifiers is active at any time, and such that the first amplifier outputs the amplified Ip and amplified In signals for a first 25% of a cycle, the second amplifier outputs the amplified Qp and amplified Qn signals for a subsequent second 25% of the cycle, the first amplifier outputs the amplified Ip and amplified In signals for a subsequent third 25% of the cycle, and the second amplifier outputs the amplified Qp and amplified Qn signals for a final 25% of the cycle; and
a differential combiner configured to combine the amplified signals output by the first and second amplifiers during the cycle to generate the RF analog signal representative of the baseband digital value.

### Claim 2 (depends on 1)

The digital-to-analog upconverter of claim 1 wherein the first and second balanced upconverters receive power from a first power supply, and wherein the first and second amplifiers receive power from a separate second power supply.

### Claim 3 (depends on 1)

The digital-to-analog upconverter of claim 1 wherein the differential combiner comprises a balun having first and second windings, wherein the first In-phase and Quadrature amplifier outputs couple to a first end of the first winding, the second In-phase and Quadrature amplifier outputs couple to a second end of the first winding, a first end of the second winding couples to ground, and a second end of the second winding couples to a digital-to-analog upconverter output to output the RF analog signal.

### Claim 4 (depends on 1)

The digital-to-analog upconverter of claim 1 wherein the differential combiner comprises a differential inductor having first and second inductor-capacitor resonators connected in parallel, wherein the first In-phase and Quadrature amplifier outputs couple to a first end of the first inductor-capacitor resonator, the second In-phase and Quadrature amplifier outputs couple to a first end of the second inductor-capacitor resonator, and wherein the first end of the first inductor-capacitor resonator is configured to output a positive portion of the RF analog signal and the first end of the second inductor-capacitor resonator is configured to output a negative portion of the RF analog signal.

### Claim 5 (depends on 1)

The digital-to-analog upconverter of claim 1 wherein the first and second amplifiers comprise common source amplifiers.

### Claim 6 (depends on 1)

The digital-to-analog upconverter of claim 1 further comprising a pre-compensation unit operatively connected to an input of each of the first and second balanced upconverters and configured to pre-distort the In-phase and Quadrature portions of the baseband digital value based on an expected distortion incurred during the digital-to-analog upconversion and based on a desired linearity requirement for the RF analog signal to generate a pre-distorted In-phase portion of the baseband digital value and a pre-distorted Quadrature portion of the baseband digital value, wherein the first balanced upconverter is configured to convert the pre-distorted In-phase portion of the digital value and wherein the second balanced upconverter is configured to convert the pre-distorted Quadrature portion of the digital value.

### Claim 7 (depends on 1)

The digital-to-analog upconverter of claim 1 further comprising an oscillator unit configured to output one or more local oscillator signals at the radio frequency for application to the first and second upconverters, wherein the one or more local oscillator signals applied to the second upconverter are out-of-phase with the one or more local oscillator signals applied to the first upconverter.

### Claim 8 (depends on 7)

The digital-to-analog upconverter of claim 7 wherein the oscillator unit is further configured to output a first and second amplifier enable signal at twice the radio frequency, and wherein the first and second amplifier enable signals are respectively applied to the first and second amplifiers to implement the interleaved output operations.

### Claim 9 (depends on 7)

The digital-to-analog upconverter of claim 7 wherein the first balanced upconverter comprises:
a plurality of In-phase conversion units, one for each digital signal of the In-phase portion of the baseband digital value, each In-phase conversion unit comprising:
a first I-branch configured to output a first weighted I-signal responsive to a first reference signal, the one or more oscillator signals, the corresponding input digital signal, and a sign of the baseband digital value;
a second I-branch configured to output a second weighted I-signal responsive to a second reference signal, the one or more oscillator signals, the corresponding input digital signal, and the sign of the baseband digital value;
a first In-phase combining node to combine the first weighted I-signals to generate Ip; and
a second In-phase combining node to combine the second weighted I-signals to generate In; and
wherein the second balanced upconverter comprises:
a plurality of Quadrature conversion units, one for each digital signal of the Quadrature portion of the baseband digital value, each Quadrature conversion unit comprising:
a first Q-branch configured to output a first weighted Q-signal responsive to the first reference signal, the one or more out-of-phase oscillator signals, the corresponding input digital signal, and a sign of the baseband digital value;
a second Q-branch configured to output a second weighted Q-signal responsive to the second reference signal, the one or more out-of-phase oscillator signals, the corresponding input digital signal, and the sign of the baseband digital value;
a first Quadrature combining node to combine the first weighted Q-signals to generate Qp; and
a second Quadrature combining node to combine the second weighted Q-signals to generate Qn.

### Claim 10 (depends on 9)

The digital-to-analog upconverter of claim 9 wherein the oscillator unit outputs a first local oscillator signal and an inverted version of the first local oscillator signal, and wherein In, Ip, Qp, and Qn each comprise a weighted average of the first local oscillator signal and the inverted version of the first local oscillator signal.

### Claim 11 (depends on 9)

The digital-to-analog upconverter of claim 9 wherein the baseband digital value represents a binary number having a plurality of bits, where each bit of the binary number has a relative binary weight corresponding to the bit position within the binary number, and wherein a weighting factor of each conversion unit corresponds to the relative binary weight of the corresponding input bit.

### Claim 12

A method of converting a baseband digital value to a radio frequency (RF) analog signal comprising:
converting an In-phase portion of the baseband digital value to a first In-phase analog component (Ip) at a radio frequency and a second In-phase analog component (In) at the radio frequency, where In is phase-shifted relative to Ip;
converting a Quadrature portion of the baseband digital value to a first Quadrature analog component (Qp) at the radio frequency and a second Quadrature analog component (Qn) at the radio frequency, where Qn is phase-shifted relative to Qp;
amplifying Ip and In using a first amplifier to generate amplified Ip and In signals at first and second In-phase amplifier outputs;
amplifying Qp and Qn using a second amplifier to generate amplified Qp and Qn signals at first and second Quadrature amplifier outputs;
wherein amplifiers used to amplify the Ip, In, Qp, and Qn signals operate at a 50% duty cycle and in an interleaved fashion such that only one of the first and second amplifiers is active at any time, and such the first amplifier outputs the amplified Ip and amplified In signals for a first 25% of the cycle, the second amplifier outputs the amplified Qp and amplified Qn signals for a subsequent second 25% of the cycle, the first amplifier outputs the amplified Ip and amplified In signals for a subsequent third 25% of the cycle, and the second amplifier outputs the amplified Qp and amplified Qn signals for a final 25% of the cycle; and
combining the amplified signals output during the cycle to generate the RF analog signal representative of the baseband digital value.

### Claim 13 (depends on 12)

The method of claim 12 further comprising powering the conversion operations with a first power supply, and powering the amplification operations with a separate second power supply.

### Claim 14 (depends on 12)

The method of claim 12 wherein combining the amplified signals comprises combining the amplified signals using a balun comprising first and second windings by:
coupling the first In-phase and Quadrature amplifier outputs to a first end of the first winding;
coupling the second In-phase and Quadrature amplifier outputs to a second end of the first winding;
coupling a first end of the second winding to ground; and
coupling a second end of the second winding to a digital-to-analog upconverter output to output the RF analog signal.

### Claim 15 (depends on 12)

The method of claim 12 further comprising pre-distorting the In-phase and Quadrature portions of the baseband digital value based on an expected distortion incurred during digital-to-analog upconversion and based on a desired linearity requirement for the RF analog signal to generate a pre-distorted In-phase portion of the baseband digital value and a pre-distorted Quadrature portion of the baseband digital value, wherein converting the In-phase and Quadrature portions of the baseband digital value comprises converting the pre-distorted In-phase and Quadrature portions of the digital value.

### Claim 16 (depends on 12)

The method of claim 12 further comprising generating an amplifier enable signal at twice the radio frequency, and enabling the first and second amplifiers using the amplifier enable signal to implement the interleaved amplifier operations.

### Claim 17 (depends on 12)

The method of claim 12 further comprising generating one or more local oscillator signals at the radio frequency, wherein converting the In-phase and Quadrature portions of the baseband digital value comprises converting the In-phase portion of the baseband digital value based on the one or more local oscillator signals and converting the Quadrature portion of the baseband digital value based on an out-of-phase version of the one or more local oscillator signals.

### Claim 18 (depends on 17)

The method of claim 17 wherein converting the In-phase portion of the digital baseband value comprises:
for each of a plurality of digital signals of the In-phase portion of the baseband digital value, generating a first weighted I-signal responsive to a first reference signal, the one or more oscillator signals, the corresponding input digital signal, and a sign of the baseband digital value, and generating a second weighted I-signal responsive to a second reference signal, the one or more oscillator signals, the corresponding input digital signal, and the sign of the baseband digital value;
combining the first weighted I-signals to generate Ip;
combining the second weighted I-signals to generate In;
for each of a plurality of digital signals of the Quadrature portion of the baseband digital value, generating a first weighted Q-signal responsive to the first reference signal, the one or more out-of-phase oscillator signals, the corresponding input digital signal, and a sign of the baseband digital value, and generating a second weighted Q-signal responsive to the second reference signal, the one or more out-of-phase oscillator signals, the corresponding input digital signal, and the sign of the baseband digital value;
combining the first weighted Q-signals to generate Qp; and
combining the second weighted Q-signals to generate Qn.

### Claim 19 (depends on 18)

The method of claim 18 wherein generating one or more local oscillator signals comprises generating a first local oscillator signal and an inverted version of the first local oscillator signal, and wherein In, Ip, Qp, and Qn each comprise a weighted average of the first local oscillator signal and the inverted version of the first local oscillator signal.

### Claim 20 (depends on 18)

The method of claim 18 wherein the baseband digital value represents a binary number having a plurality of bits, and each bit of the binary number has a relative binary weight corresponding to the bit position within the binary number, and wherein each weighted I-signal and weighted Q-signal is weighted according to a weighting factor corresponding to the relative binary weight of the corresponding input bit.