Texas Instruments TRF370 Series User manual

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
3
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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.
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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.
(c) Verify that the current draw is ≤205 mA for the TRF370x1x and ≤235 mA for the TRF370333.
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.
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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.
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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.
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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).
9
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DAC56x2 TRF370315
I I
Q
S0225-02
Q
II
QQ
R2
R2
R2
R2
5 V
5 V
R1
R1
R3
R3
R1
R1
R3
R3
DAC568x TRF370333
I I
S0226-02
II
R5
R5
5 V
5 V
R6
R1
R1
R3
R3
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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
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