Radar System Engineering

SEC. 13.9] ELECTRONIC SWITCHES 505
input of the circuit, the time elapsing before an output signal appears is
proportional to the bias applied to the diode, thus providing an accurate
and easily controllable time delay (see Sec. 13.12).
Switched Clamps.—In a great many applications
the clamp must be opened and closed
over particular time intervals which may or /lA-&,.o
may not be directly related to the signals.
~!?~o
According to whether the clamp can conduct
in one or both directions when c1osed it is
classified as a one-way-(” single-sided”) or a
two-way (” double-sided”) clamp.
FIG, 13.22.—Bottom clipper
(biased diode ‘: pick-off”
In the diagrams, E, is the potential of the circuit).
clamping point, X is the point being clam~ed,
A is the maximum signaiamplitud~, and “Tis the time interval over which
the clamp is to be opened. If E, is not ground potential, the voltage
t+
i
R,
Ex 2 EO
(c)
(a)
(b)
+- ..!..
FIG. 13.23.—One-way switched-diode clamps. (a) Switched single diodes; (b) double.
diode clamps; (c) diode switched by cathode follower.
X is point being switched. T is length of open interval.
A is maximum amplitude of signal at X. R must be very high.
Eo is clamping potential. Plus and minus signs are with respect to 130.
source supplying the clamping point must be “ stiff” enough to fllrnish
the currents drawn without appreciable potential change.
Among the simple switched clamps are the diodes of Fig. 13.23a, the