AN2472

STMAV340 measurement set up

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STMAV340 measurement set up

2.1

Calibration

This is one of the most critical parts to good measurement. The AC parameters of the switch

are measured using a network analyzer which must be properly calibrated before use. The

calibration is done on the equipment itself and then with the board. Through, open and short

calibration are performed without the DUT placed on the board or with DUT enabled on the

board and with both the input and output ports of the network analyzer connected to the

switch connectors on the board. After the calibration is done, the channel output on the

analyzer is stable and is not affected by any movements of the cables or the board. This

also helps to ensure that the calibration is performed by taking the DUT and board into

account. Initially if desired the calibration can be run by connecting the two ports together.

2.2

Termination for bias

In a typical video application the bias is needed to provide the DC offset required for the

video signal. The decoupling capacitor filters the negative part of the video signal before it

reaches the switch. The inputs and outputs of the switch have to be terminated with 75 Ohm

resistors to eliminate any reflections due to impedance mismatches between the source and

the sink.

The parameters are measured with 150 Ohm load as the series resistor of 75 Ohm of the

cable is in series with the far-end termination resistor of 75 Ohm, adding them up to

150 Ohm.

2.3

Measurement techniques

Proper measurement methods and stable test set-up ensure that the real device parameters

are measured during the characterization of the device. Good contacts of the cable

assemblies to the SMA connectors on the board must be present. Care is taken to ensure

that the probes of the equipment are tightly screwed to the equipment and the device under

test (D.U.T.). Soldering with a good shining solder dot without any dry solder gives a robust

low resistance contact for the signals on the board.