LA7770
In the Fig. 6 phase shifter,
1
V2 =
jωC2+
1
R
+jwL
=
1
V1
1
jωC1
+
jωC2+
1
1
R
+jwL
ω2L (C1+C2)–1 –j 1
ω2LC1
jωCR
Requirements to achieve a 90° phase shift will be :
ω2L (C1+C2)=1
∴ƒ=
1
2π√L (C1+C2)
ω=
1
√L (C1+C2)
V2 =
1
V1
√
ω2L (C1+C2)–1
2
+
1
2
ω2LC1
jωC1R
At the tuning point :
V2 =
√ V1
1
1
2
ωC1R
=ωC1R
(5) Meter Drive and Squelch
A forward bias is provided to the meter drive dedicated detector, to enable its detector diode to detect low-level
signals. In addition, a bias canceler is also provided to eliminate the offsetting current in a no-signal mode created
by the forward bias. Furthermore, to broaden the linear operating range, signals are fetched from the 3rd and 5th
stage outputs of the limiter amplifier, for composition together after level detection.
Fig. 7
No.2208–5/7