AN3629| Application Note
Maxim/Dallas > App Notes > AUTOMATIC TEST EQUIPMENT (ATE) HIGH-SPEED INTERCONNECT
COMMUNICATIONS CIRCUITS
Keywords: power detector, gain, calibration, slope, coupler losses, heterodyne transceiver, transmitter, receiver, ATE, log detector, VGA, VVA, RF detector, offset, log detector
Sep 02, 2005
APPLICATION NOTE 3629
Techniques for Measuring RF Gain Using the MAX2016
This application note discusses how to implement the MAX2016 RF detector into an automated test system for gain measurements in heterodyne transceiver applications. The article compares the quality and measurement accuracy from three different approaches: gain measurement and calibration; gain measurement with offset only; and gain measurement with offset and slope calibration.
Introduction
As a dual RF power detector, the MAX2016 is quite capable of performing gain measurements for single RF blocks or more complex heterodyne transceiver lineups. One of the part's key features is the inclusion of an on-chip comparator circuit, which computes the difference between the two applied power levels.A simple gain calculation of gain = POUTPUT - PINPUT = POUTA - POUTB = POUTD is easily realized through this circuitry. Care must be taken, however, to ensure that the accuracy requirements of the measurement are adequately met. Depending on the application, a one-time calibration may be needed to counter any differences in line and coupler losses, as well as part-to-part variations. The following application note outlines some basic calibration methodologies employed in RF gain measurements. Two common applications are presented. The first example is a detailed look at measuring the gain of a heterodyne transceiver. The second example shows how the calibrated MAX2016 can replace slow and expensive power m
eters in factory Automated Test Equipment (ATE) applications. In the ATE example, a comparison of the accuracy achieved with and without calibration is provided for reference. Both examples demonstrate the importance of adequately calibrating the measurement setup.
Typical RF Transceiver Gain Measurements
Because the MAX2016's power detectors possess an extended frequency range of DC to 2.5GHz, the device can easily be configured to measure the gain of either a single gain block (Figure 1a) or a complete heterodyne receive/transmit lineup (Figure 1b).
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