Texas Instruments TRF370 Series Manual de usuario

TRF370x Quadrature Modulator Evaluation

Module

User's Guide

Literature Number: SLWU062

March 2010

2SLWU062–March 2010

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1 Overview ............................................................................................................................ 5

1.1 Purpose ................................................................................................................... 5

1.2 EVM Circuit Overview ................................................................................................... 5

1.3 Power Requirements .................................................................................................... 5

1.4 TRF370x EVM Operating Procedure ................................................................................. 6

2 Physical Description .......................................................................................................... 11

2.1 PCB Layout ............................................................................................................. 11

2.2 Parts List ................................................................................................................ 16

3 Circuit Description ............................................................................................................. 16

3.1 Circuit Function ......................................................................................................... 16

4 Circuit Board .................................................................................................................... 17

5 Schematic ......................................................................................................................... 18

SLWU062–March 2010 Table of Contents

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List of Figures

1 Unadjusted Sideband Suppression....................................................................................... 7

2 Optimized Sideband Suppression ........................................................................................ 8

3 GSM EDGE EVM at 1800 MHz........................................................................................... 9

4 1.5-V Interface Network for 19.2 mA Full Scale....................................................................... 10

5 3.3-V Interface Network for 19.2 mA Full Scale....................................................................... 10

6 Top Layer 1 ................................................................................................................ 11

7 Top Layer 2 ................................................................................................................ 12

8 Ground Plane 1............................................................................................................ 12

9 Ground Plane 2............................................................................................................ 13

10 Bottom Layer 1............................................................................................................. 13

11 Bottom Layer 2............................................................................................................. 14

12 Drill Pattern................................................................................................................. 15

13 Silkscreen Top Layer ..................................................................................................... 17

14 TRF370x EVM Schematic................................................................................................ 18

List of Tables

1 Bill of Materials for TRF370x EVM...................................................................................... 16

2 Power Supply Connection................................................................................................ 17

4List of Figures SLWU062–March 2010

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User's Guide

SLWU062–March 2010

TRF370x Quadrature Modulator Evaluation Module

1 Overview

This document relates to the TRF370x direct quadrature modulator for applications in the transmit path of

base stations and communications equipment. The quadrature modulator is used for upconversion of

signals from the transmit chain DAC to the RF power amplifier device. Evaluating modulator complex

performance involves careful bias-voltage setup, an LO signal, and two differential (I/Q) signals at the

input of the modulator. This document describes the wide range of test options available and the factors

that must be considered in using this EVM.

1.1 Purpose

The TRF370x evaluation module (EVM) is intended for the evaluation of the TRF370333, TRF370317,

TRF370315, and TRF370417 direct-launch quadrature modulators. Unless otherwise stated, the

functionality described in this manual applies to all the TRF370x devices.

1.2 EVM Circuit Overview

The EVM comes configured for differential I/Q input signals via four SMA connectors as shown in the

schematic, Figure 14, and in Table 1.

For the upper sideband, the I signals are connected to J4 (I+) and J3 (I–). The Q signals are connected to

J5 (Q–) and J6 (Q+). The LO signal is fed to SMA connector J1, whereas J2 must be terminated with 50 Ω

to ground. SMA connector J7 is used to monitor the RF output signal from the quadrature modulator (U1).

The quadrature modulator requires a supply voltage of 4.5 V–5.5V from a regulated power supply through

headers TP2 and TP4.

The TRF370x quadrature modulators require a dc common-mode bias voltage (3.3 VDC, 1.7 VDC, or 1.5

VDC, corresponding to the last two digits of the part number) on all four input pins.

1.3 Power Requirements

The TRF370x EVM requires two 5-V VCC dc power-supply connectors through headers TP2 and TP4.

Header TP4 supplies 5 V to the LO circuitry, and TP2 supplies 5 V to the modulator circuitry.

CAUTION

Voltage Limits

Exceeding 5.6 V may damage the TRF370x.

SLWU062–March 2010 TRF370x Quadrature Modulator Evaluation Module

Overview

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1.4 TRF370x EVM Operating Procedure

Set up the EVM as follows:

1. Power-supply connection:

(a) Switch on the VCC (5-V) supply and set the current limit to 235 mA.

(b) Connect the 5-V supply to headers TP2 and TP4. Connect ground to TP1 and TP3.

2. Use a suitable 50-Ωoutput signal generator or the TRF3761 to supply the LO signal at the desired

frequency to J1, and terminate J2 with 50 Ωto ground.

3. Use a DAC or an arbitrary waveform generator to provide the I/Q input signals. A typical setup is as

follows: a 1-Vp-p sine wave, a frequency of 50 kHz, a dc offset of 0 V, and an output impedance of

50 Ω(typically an ESG vector signal generator or similar).

4. Set the common mode on the ESG to either 1.65 V, 0.75 V, or 0.85 V, depending on device type (set

to 1.65 V for the TRF370333, to 0.75 V for the TRF370315, or to 0.85 V for the TRF370x17).

5. Use an arbitrary waveform generator to suppress the sideband. Adjust the I/Q amplitude and phase of

the CW signal coming from the arbitrary waveform generator.

6. Connect a spectrum analyzer to the SMA connector marked RFOUT (J7) and monitor the TRF370x

output.

1.4.1 Typical Test Results

1.4.1.1 Unadjusted Sideband Suppression

Unadjusted sideband suppression measures the amount of the unwanted sideband of the input signal,

relative to the wanted sideband. This assumes that the baseband inputs delivered to the modulator input

pins are perfectly matched in amplitude and are exactly 90° out of phase. Unadjusted sideband

suppression is measured in dBc. An iterative test is required in order to match perfectly the inputs to the

modulator. This ensures that any equipment, board, or signal conditioning component imbalances are

corrected before the signals are applied to the device under test. Once the baseband inputs to the

modulator are balanced, the amount of suppression attained is a measure of the internal mismatches of

the modulator, inherent to any modulator design. This suppression is the one specified in the TRF370x

data sheet. See Figure 1.

6TRF370x Quadrature Modulator Evaluation Module SLWU062–March 2010

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Overview

Figure 1. Unadjusted Sideband Suppression

1.4.1.2 Optimized Sideband Suppression

The sideband suppression of the TRF370x can be optimized by adjusting the amplitude and phase

balance between the quadrature inputs. The ideal condition is when all four inputs (I, I, Q, and Q) have

exactly the same amplitude and the phase relationship is: I = 0°, I = 180°, Q = 90°, and Q = 270°. Using

an iterative procedure, the gain and phase balance can be adjusted to achieve suppression levels that

exceed 60 dBc. The level of suppression observed depends on the amount of resolution available from

the source driving the modulator. By using TI’s DAC568x, the user can take advantage of built-in features

to optimize the sideband suppression by changing the amplitude and phase relationship of the signals. If

another DAC is used, then the user must provide this level of adjustment by controlling the regular digital

inputs to the DAC. See Figure 2.

SLWU062–March 2010 TRF370x Quadrature Modulator Evaluation Module

C002

Overview

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Figure 2. Optimized Sideband Suppression

1.4.1.3 Carrier Feedthrough

Carrier feedthrough is the amount of the LO that leaks onto the output spectrum of the modulator. Ideally

for the TRF370x, inputs (I, I, Q, and Q) must be at approximately 3.3 V for TRF370333, 1.5 V for

TRF370315, and 1.7 V for TRF370317 and TFR370417. The DAC dc settings are also useful to correct

the dc mismatch between I and I and between Q and Q to minimize the LO feedthrough. If using TI's

DAC568x, then the internal controls for the I/Q offsets provide excellent carrier suppression (very low LO

leakage). Alternatively, if an ESG is being used, adjust the I and Q voltage offsets in mV steps until you

obtain the minimum carrier feedthrough. A typical carrier feedthrough value exceeds –50 dBm. See

Figure 2.

1.4.1.4 GSM (EDGE EVM Measurements)

1. Provide a GSM edge signal of the desired frequency into the differential baseband inputs (example

sample rate = 4.33 MHz).

2. Use a spectrum analyzer with edge personality to measure the transmit power to either 0 or –5 dBm.

3. PSA: Mode →GSM (with EDGE) →measure →Transmit Pwr (usually 0 or –5 dBm) →more →

EDGE EVM.

4. ESG: Mode setup →select waveform →highlight EDGE →select waveform →ARB setup →type

4.33333 MHz →I/Q →I/Q output control →Common mode I/Q offset →(set to 1.65 V, 0.75 V, or

0.85 V, depending on device) →I/Q →I/Q output control →I/Q output atten (adjust to get desired

transmit power to either 0 or –5 dBm).

See Figure 3.

8TRF370x Quadrature Modulator Evaluation Module SLWU062–March 2010

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Overview

Figure 3. GSM EDGE EVM at 1800 MHz

1.4.2 Interface to TI's DAC

All the TRF370x devices work well with TI's DACs. Figure 4 shows an example of the interface network

between a DAC56x2 and a TRF370315. Figure 5 shows an example of interfacing the DAC568x to the

TRF370333 with options for selecting the desired amount of attenuation between the two. Additional

interfacing networks for each modulator can be found in their respective data sheets or by using the DAC

interface calculator (SLWC083).

SLWU062–March 2010 TRF370x Quadrature Modulator Evaluation Module

DAC56x2 TRF370315

I I

S0225-02

5 V

DAC568x TRF370333

I I

S0226-02

5 V

Overview

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TYPICAL VALUES

R1 R2 R3

53 Ω210 Ω931 Ω

NOTE: A DAC interface calculator is available (SLWC083).

Figure 4. 1.5-V Interface Network for 19.2 mA Full Scale

LOSS 1 dB 2 dB 3 dB 4 dB 5 dB

Pullup R1 115 115 115 115 115

Pulldown R3 634 634 634 634 634

Series R5 11 21 30 37.4 45.3

Shunt R6 187 165 147 130 118

Figure 5. 3.3-V Interface Network for 19.2 mA Full Scale

10 TRF370x Quadrature Modulator Evaluation Module SLWU062–March 2010

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