Yijun Zhou, Department of Electroscience, Lund University, Sweden

An Direct Digital RF Quadrature Modulator

Yijun Zhou and Jiren YuanCompetence Center for Circuit Design

Department of ElectroscienceLund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Overview

1. The purposes of this design.2. The traditional direct-conversion modulator and the

Gilbert cell mixer.3. The proposed direct digital RF quadrature modulator

architecture and design.4. Measurement results.5. Conclusion.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

LPF

cos(ct)sin(ct)

I

Q

DAC

Out

DAC

LPFdirect-conversion modulator

The traditional direct-conversion modulator.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

RF

Linear Interpolation DAC

Data

The block diagram of the direct digital RF amplitude modulator.

Linear Interpolation DAC

cos(ct)sin(ct)

Out

Linear Interpolation DAC

I

Q

The direct digital RF quadrature modulator.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

RF+ RF-

R1 R2Vout

Vb+ Vb-

Bias

The Gilbert cell mixer.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

RF+ RF-

R1 R2Vout

Ib+ Ib-

Yijun Zhou, Department of Electroscience, Lund University, Sweden

RF+ RF-

Linear Interpolation Current Steering DAC

I+ I-

Vbias Vbias

R1 R2Vout

Gilbert cell

The direct digital RF amplitude modulator.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

RFI+ RFI-

Linear Interpolation Current Steering DAC

I+ I-

VIbias

R1 R2

The direct digital RF quadrature modulator.

RFQ+ RFQ-

Linear Interpolation Current Steering DAC

I+ I-

VQbias

Yijun Zhou, Department of Electroscience, Lund University, Sweden

X(f)

-fs fs f

Zero-order hold

Linear interpolation

The spectrum of the sampled digital signal, the frequency response of a zero-order-hold DAC and a linear interpolation DAC.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Clk B0 B1 B2 B3 B4 B5 B6 B7

C1C2C3C4C5C6C7C8C9C10C11C12C13C14C15C16

2x0.5I

2I

4I

8I

16I

16x2I

16x4I

16x8I

Clock Delay Unit

B8 B916x16I

16x32I

Sub-Current Source Unit

Load

I One LSB Current

The 10-Bit, 16-tap linear interpolation DAC.

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

Yijun Zhou, Department of Electroscience, Lund University, Sweden

CONCLUSION1. The direct digital RF quadrature modulator can be

realized without LPF using the linear interpolation DAC.

2. The direct digital RF quadrature modulator can simplify the RF transmitter design and be scalable easily.