Agilent Technologies 8753ES, Service Manual

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Chapter 12 12-25
Theory of Operation
Signal Separation (8753ES)
Signal Separation (8753ES)
The Built-In Test Set
Figure 12-11 shows a simplified block diagram of the analyzer’s built-in test set.
A21 and A22 Test Port Couplers
The analyzer’s test port couplers are used to separate signals incident to, reflected from,
and transmitted from the device under test. Each test port coupler has a coupling
coefficient factor of 16 dB.
A23 LED Front Panel
The LED front panel board indicates whether the source power is incident on the
analyzer’s test port 1 or test port 2. The analyzer’s source power is directed to test port 1
when making a forward transmission/reflection measurement. Similarly, source power is
incident at test port 2 when making a reverse transmission/reflection measurement.
A24 Transfer Switch
The A3 source output power is directed to either the analyzer’s test port 1 or test port 2 via
a low loss solid state transfer switch. With this switch, all four S-parameters can be
updated continuously (for example, the data obtained from a full 2-port calibration). In
addition, the transfer switch provides termination for the inactive test port in order to
minimize the crosstalk between the source and receiver sampler.
A25 Test Set Interface
The test set interface board provides biasing for active devices under test with an external
dc voltage. This dc voltage is applied directly to the test port center pin. In addition, the
test set interface board provides the drive signal for the A24 forward/reverse transfer
switch.