HP 8754A - Test Setup; Transistor Bias

VCB
Programming
Interconn
) >-----,
Bridge A
Bias 2
Port 2
.L" Connect
" Short
Common
Base
Connect "\..
Short .,
8754A
Model 8754A
I/~ Ten ~\\
I DeVice \
I \
L - - - - --Connect--- --- - ~
Together
To Calibrate
Transmission
Port 1
r---7>
A Bridge
Bias
1
26
+
>---<
Bridge
Port 2 Bias 2
VCB
I
Common
Emitter
L-- ----~ PS2
BRIDGE BIAS 1 and 2 on the 8748A rear panel provide connections for ±30 Vdc, ±200 rnA bias when
measuring transistors.
For the common emitter, choose R
E
for desired collector current with maximum voltage drop across R
E
while
maintaining forward bias voltage. (For example, with IE = 20 rnA, RE~ (IOV /0.02) = 5000.)
Choose R
B
to control oscillations (typically from 100 to 4000). Turn on PS2 first and set voltage to V CE +
I
R
drop across R
E
, then turn on PSI and set for desired IE.
With the correct matched test port extension cables or fixture
and reference plane extension installed, the test setup has
nearly equal losses and electrical lengths for both forward
and reverse measurements. This allows forward transmission
and reflection calibrations to be used for both forward and
reverse measurements. If other than the listed fixtures are
used, then the reference and test signal paths must be matched
to achieve a symetrical test setup.
Transistor Bias
Use a
dual dc power supply such as the HP Model 6205B that is designed for use with bias tees optimized
for RF applications. (The HP Model 87l7B Transistor Bias Supply is not compatible with the 8748A; it is
designed
for bias tees optimized- for microwave frequencies and may cause the test device to oscillate).
These diagrams show biasing connections for NPN common emitter and common base configurations.
Reverse power supply polarities for PNP devices.
For the common base, choose R
E
as above and R
B
is not required. Turn on PS2 first and set to V CE + I
R
drop across R
E
, then turn on PSI and set for desired IE. Finally reset PS2 for desired VCB.
Connections to the test device can be made using the 11857 A
Test Port Extension Cables, or the 11608A, 11600B, or
11602B Transistor Fixtures. The rear panel Reference Plane
Extension cable
must be matched to the test fixture in order
to equalize the signal paths. The table on Page 5 lists the
reference plane extension cable which should be used with
each fixture. Note that the signal path lengths from ports
1 and 2 must be equal.
S-Parameter Measurements
Test Setup
This diagram shows
connections using the 8748A S-Param-
eter Test Set. Use the four 19 cm Type N cables supplied
to connect the RF, R, A, and B ports on the 8748A and
8754A front panels. The cable between the 8754A and
the upper 8748A PROGRAMMING connector is required
for proper operation of the network analyzer and test set
combination.
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