value
of
one
capacitor. Fig.4.23 shows
the
"Peak"
response and
the
possible
options
with various
time
constants
(r).
Fig.4.24 shows
the
value
of
t
the
necessary charge capacitor
vs
the
time
constant.
4.12. VOLTAGE SUPPLY
The
voltage supply
is
designed as a
DC
to
DC
converter and delivers
both
stabilised and unstabilised voltages
to
the
amplifier circuits. A
correct
volt-
age can be supplied from
any
battery
voltage
between
3 and
4.6
V. For
the
internal reference voltage, a square wave generator
of
frequency 2 kHz
is
included.
+360V
Fig.4.25. Polarization Voltage supply
circuit
The
polarization voltage for
the
microphone
is
produced by voltage
doublers
and
is
regulated with a Zener diode as shown in Fig.4.25.
The
temperature
coefficient
of
the
Zener
diode
is
approx. 100
mV
/°C
or
about
0.05%/°C.
The
correction due
to
change
in
temperature
is
seen
in
Fig.4.26.
0.5
~
+0.25
~---
~
-20
-10
0
+Jo----+20
+ 30
+40 +50
0
2l
---~
Ql
::!:
-0.25
0.5
Fig.4.26. Temperature correction
for
polarization voltage
46
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