Linear Technology DC651A User manual

DC651A DEMO BOARD QUICK START GUIDE
Description:
The DC651A demo circuit board is intended to demonstrate the capabilities of the LT5522 high-
signal-level downconverting mixer IC for cable and CATV infrastructure applications.
The LT5522 (Figure 1) is a broadband high signal level active mixer optimized for high linearity
downconverter applications including cable (CATV) and wireless infrastructure. The IC includes a
high-speed differential LO buffer amplifier driving a double-balanced mixer. The LO buffer is
internally 50ohm-matched for wideband, single-ended operation with no external components.
The LT5522 IC’s RF input port incorporates an integrated transformer and is internally matched to
50ohms over the 1.2GHz to 2.3GHz frequency range. The RF input match can be shifted down to
600MHz, or up to 2.7GHz, with a single shunt capacitor or inductor, respectively. The high level of
integration minimizes the total solution cost, board space and system-level variation.
The LT5522 delivers high performance and small size without excessive power consumption.
The DC651A demo board allows evaluation of the LT5522 downconverting mixer IC for cable
infrastructure applications. Its RF input is optimized for 1150MHz. The IF output frequency range
spans 50MHz to 1050MHz. The corresponding range of LO frequencies is 1200MHz to 2200MHz.
Figure 1. LT5522 IC Block Diagram

LT5522 Downconverting Mixer Single-Tone Measurements for CATV Band.
1. Connect all test equipment as shown in Figure 2.
2. Set the Power Supply voltage to 5V, and set the current limit to 100mA.
3. Connect TP1 (EN) to the 5V power supply; the mixer is enabled (on).
4. Set the Signal Generator #1 to provide a -5dBm CW signal, at the desired LO frequency
between 1200MHz and 2200MHz (e.g., 1650MHz), to the demo board LOin port.
5. Set the Signal Generator #2 to provide a 1150MHz, -12 dBm CW signal to the demo board
RFin port.
6. Set the Spectrum Analyzer center frequency to the IF output frequency at fLO-fRF
(e.g., 500MHz). Perform mixer conversion gain, and 1dB compression measurements.
7. Set the Spectrum Analyzer center frequency to the LO frequency (e.g., 1650MHz). Perform
mixer LO to IF leakage measurement.
SPECTRUM
ANALYZER
SIGNAL
GENERATOR 1
SIGNAL
GENERATOR 2
POWER SUPPLY
Figure 2. Test Set-Up for Mixer Single-Tone Measurements.

LT5522 Downconverting Mixer Two-Tone Measurements for CATV Band.
1. Connect all test equipment as shown in Figure 3.
1). Use high quality signal generators with low harmonic output for this measurement.
Otherwise, low-pass filters should be used to suppress harmonics.
2). A high quality combiner that provides 50ohm termination on all ports and has good
port-to port isolation should be used.
3). The two 3dB attenuators on the inputs of the combiner are used to further improve
source isolation.
2. Set the Power Supply voltage to 5V, and set the current limit to 100mA.
3. Connect TP1 (EN) to the 5V power supply. Mixer is enabled (on).
4. Set the Signal Generator #1 to provide a -5dBm CW signal, at the desired LO frequency
between 1200MHz and 2200MHz (e.g. 1650MHz), to the demo board LOin port.
5. Set the Signal Generator #2 and #3 to provide two -12dBm CW signals to the demo board
RFin port—one at 1150MHz, and the other at 1151MHz.
6. Set the Spectrum Analyzer center frequency to the IF output frequency at fLO-fRF. Perform
input 3rd order distortion measurement (i.e. IIP3 = P1+ (P1– P3) / 2 – Gc, where P1is the
lowest power level of the two desired output tones at either 499MHz or 500MHz, P3is the
largest 3rd order product at either 498MHz or 501MHz, and Gc is conversion gain. P1and
P3 are in units of dBm, and Gc is in dB).
SPECTRUM
ANALYZER
SIGNAL
GENERATOR 1
SIGNAL
GENERATOR 2
POWER SUPPLY
SIGNAL
GENERATOR 3
∑
3dB PAD
3dB PAD
Figure 3. Test Set-Up for Mixer Two-Tone Measurements.