Stanford Research Systems
13
10MHz Distribution Amplifiers
provide very large channel-to-channel isolation. The emitter of the third follower drives a 2:1
output transformer via a series R-C (R219 & C212) to reduce the output impedance by 4:1 in
order to drive a 50
Ω
load. The 50
Ω
user load is driven via a low-pass filter. The filter has a
pass-band to 11.5MHz and a notch at 20MHz in order to eliminate harmonic distortion at the
output.
Status LEDs.
The input level detector is used to detect signal levels which are too small or
too large. The detector, D100, is a dual Schottky diode that is biased “on” by R104, R105
and R107. (Biasing the detector “on” improves its ability to detect low signal levels.) The
output of the level detector is compared with fixed thresholds by two comparators (U101).
The SIGNAL LED will be “on” for inputs greater than about 500mV
pp
and the OVERLOAD
LED will be “on” if the input signal exceeds about 5V
pp
. The user supplied 10MHz input
should be somewhere between these two levels.
The FAULT LED is controlled by U104 & U105 which turns the LED “on” if any of the
following conditions exist: no signal at the input, overload at the input, +22V supply is below
+20.5V.
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