Frequency Translation Device Measurements
RI Measurement Approach
Multi-Port S Parameter Detection Hardware 100 MHz to 20 GHz
Requires one or more additional RF Source for DUT LO
RF Stimulus Source: RF Input 100 MHz to 20 GHz
DUT LO Source: LO Input 10 MHz to 20 GHz
Maintain Constant IF Freq
Sweep RF & DUT LO Frequency
Requires 3 RF Sources to be at Different Frequencies
Measure: Pin(RF) and Pout(lF)
Calculate: Conversion Gain/Loss=Pout(lF)/Pin(RF)
Test Plan Optimizer Determines the Measurement Sequence
RI ATE systems performs highly accurate measurements on frequency translation devices such as mixers, multipliers, or any multi-port device as a series of scalar (absolute amplitude) S parameter measurements between multiple RF ports. In addition to the System Local Oscillator and the DUT Stimulus Source (Source1), these measurements require one or more RF sources for the DUT’s local oscillator (Source2, 3 or 4). RF Source 3 and Test Head port RF2 have been specially designed to work together so as to deliver maximum power to the DUT's LO port while still allowing S Parameter measurements on that port. The Cassini ATE system can test devices with many RF ports without adding more RF Test Ports to the Test Head. Devices with up to 12 RF ports can be easily tested, and devices that need more RF ports can be tested by adding RF switches to the Test Fixture. The RF stimulus frequencies and the DUT's IF frequency are specified by the user in a test plan. The system sweeps Source1 and the DUT LO frequencies and holds the DUT IF frequency constant during the measurements. All three RF sources must be set independently to different frequencies in order to make the measurements. The order in which the measurements are performed is controlled by the test plan optimizer so that measurements can be made in the fastest possible time.
The RF diagram shown represents a typical mixer conversion gain/loss measurement configuration for the RF Test Head. The RF stimulus source (Source1) is routed to the Source1 input of the Test Head through the RF Matrix Modules, so the RF stimulus signal is routed through the Test Head to the DUT’s RF input connected to port RF3. Source3 is routed to the Source3 input port through the RF Matrix Modules, so the RF signal from Source3 is connected through the Test Head to the DUTs LO input connected to the special port RF2. The mixers IF output port is connected to port RF6. The incident signal at port RF3 and the transmitted signal at port RF6 are separated and individually routed through the couplers connected to port 3 and 6, through the electronic switches (connected to the coupled arms), an electronic switch, an RF solid state step attenuator, and a RF preamplifier to the single channel System Receiver at port REC for signal processing.
If the Mixers IF frequency is below 100 MHz then its output port should be connected to the direct receive path with no frequency limiting devices, Test Head port RF4. RF4 is routed directly from the Test Head through the RF Matrix to the Low Frequency input port of the Receiver. This path has no step attenuator or LNA, for measuring S Parameters, so it will operate down to under a few kHz.
All of the signal paths through the RF Test Head are individually characterized and calibration factors are maintained for each of these paths.
S Parameters use the same measurement process as a conversion gain/loss measurement above 100 MHz. When the frequency of the IF is under 100 MHz, the direct path through RF4 is used and the signal is routed to the Low Frequency mixer input directly. If the signal level is above -23 dBm, you must attenuate the signals in the test fixture to not overdrive the Receiver's first mixer. The signal is down converted to the same 21.4 MHz IF frequency using the external System Local Oscillator connected to the LO In port. The IF signal is amplified/filtered and sent to the complex synchronous quadrature detector. The complex detector splits the received signal into two equal amplitude and equal phase signals and mixes one signal with a 21.4 MHz signal in-phase with the System Receiver’s internal 21.4 MHz SOURCE to create the I (in-phase) signal component and mixes the other signal with a 21.4 MHz signal which is 90° out of phase with the 21.4 MHz SOURCE to create the Q (quadrature) signal Component. The resulting signals are low pass filtered and sampled by the high speed sample and hold circuits. The high accuracy A to D converters digitizes the sampled I and Q signal components and send the digitized data over the RIFL II bus to the System Computer for processing. The system controller calculates the conversion gain/loss (S21 or S12 magnitude only).