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2.5.6.
Line Trigger Pick-off (see Fig.
The line trigger signal is derived from the secondary winding of the mains transformer via t h e connector
The mains voltage sine-wave signal i s applied t o the transistor V1406 via resistors R1422 and R1423. The
.-
square-wave signal
This filter re-converts the square-wave voltage t o a sine-wave voltage a t the mains frequency.
connector X858, pin 6.
2.6.
BASIC ANALOG AND DIGITAL CIRCUITS
This section describes briefly the most important characteristics of the analog and digital circuits t o be found
i n the instrument.
Basic Analog Circuits
2.6.1.
Series feedback amplifier
-
This i s also called a Cherry configuration.
A voltage signal A U is applied to the input; the output produces a current signal A1
Shunt feedback amplifier
-
This is also called a Hooper configuration.
A current signal A l is applied t o the input; the output produces a voltage signal AU
-
Series feedback amplifier followed by a shunt feedback amplifier
This combination of the two previous configurations is called a Cherry-Hooper circuit.
In
this two-stage amplifier, both the input and the output are voltage signals. The gain of this amplifier is:
Emitter-follower
-
The emitter-follower is used as an impedance converter.
The input impedance i s HIGH and the output impedance is LOW. The stage has a voltage gain of XI,
output voltage signal i s identical t o the input voltage signal.
-
This circuit consists of two emitter-followers connected in cascade.
and the output impedance low.
Again, this stage has a voltage gain of XI and the output voltage signal is identical to the input voltage signal.
Common base circuit
-
This type of circuit i s frequently used between amplifier stages for d.c. voltage level adaption or for buffering.
The input impedance is low and the output impedance is high.
It has a current gain of
-
Long-tailed pair
In the diagram of Fig. 2.12, the long-tailed pair is formed by transistors V1 and V2. Transistor V3 functions as
a constant-current source for V 1 and V2. The current drawn from V 3 is divided between V 1 and V2. the
proportion depending on the base voltages applied (U1 and U2).
The division i s as follows:
- -
8.15)
on
the collector o f V1406 is routed t o a filter consisting of R1419, R1416, R1414 and
Fig. 2.12)
(see
the output current signal being identical t o the input current signal.
RE2
A U
-
.
As
a result, the input impedance i s very high
2-33
and the
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