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t4
continuous gain control R2 is also connected to the
At frequencies where o1 Ê9 cr2 cro c (a denoting the
emitter of TS401.
desired overall gain) the output at "a" equals the
The output impedance of the two amplifiers is very
output at "b", thus no current will flow through the
small cornpared with the impedance of R216 -
interstage network. Than the output at "C" equals
C157. This means that, seen from the IIF amplifier
q Vi.
C1,57 + R216 act as a high-pass filter with a cross-
over frequency of 100 kHz, thus suppressing low
At low frequencies, a1 is smaller than a2 ànd a2
frequency noise components and other spurious low
equals a'. Now the output at "t' is smaller than the
frequency signals, generated in the tIF amplifier
output at "b" so a current will flow through R216
(Fig. 10). Seen from the LF amplifier, however,
and C157, which causes R216 - C1.57 to act as a
R216 + Cl57 act as a low-pass filter with a cross-
low-pass filter to the output at"V'. As a2 V1 : cVi
over frequency of 100 kHz, suppressing high fre-
the output at "C" equals the output at "b".
quency noise components and other high frequency
At high frequencies, o2 is smaller than a1 and u1
signals generated in the LF amplifier.
equals 61.
An input signal Vt applied to the split-band amplifier
Now the output at "b" is smaller than the output at
(see Fig. 11) causes an output sigrral c1 V1 at "a"
"a", so a current will flow through R216 and CI57,
and an output sigr.al q2 V, at "b" (ar and az de-
which causes R216 -C157 to act as a high-pass filter
noting the gain of respectively the HF amplifier and
to the output at "a". As a1 V; : cVi the output at
the LF amplifier).
63c)) equals
the output at "a"
Fig. I0.
Bandwidth characteristics
D C AMPL.
t O 3
t O 1
tO 5
tO6
4 MHz (DC-AMPL
Fig. I I . Operation of the cross-over filter
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