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V. OPERATING PRINCIPLES
OF QUADRATU RE
mpur PSI i
e a DETECTED
L-P-E . OUTPUT
Fig. 7 Quadrature Detection Block Diagram
Fig. 8 Single Tuning Type
Fig. 9 Double Tuning Type
SINGLE TUNING TYPE
INPUT e 1W“
DOUBLE TUN¥IG TYPE
Fig. 10 Tuning Curve
The Quadrature Detection Circuit is comprised of a
Phase Circuit, a Multiplier Circuit and a Low Pass Filter
(L.P.F.) as shown in Fig. 7.
There are two types of Phase Circuits, the Single tuning
type shown in Fig. 8 and the Double tuning type shown
in Fig. 9. However, because with the double tuning type
there is less frequency deviation in relation to carrier
frequency, linearity is improved as shown in Fig. 10 and
phase distortion is reduced, this type phase circuit is
employed in the AA-1115 and AA-l 125.
Input signal S! in divided into the part which enters the
direct multiplier circuit and the part which passes the
phase circuit and enters the multiplier circuit. The signal
supplied to the phase circuit as always 90° phase delayed
at Ll. Also because at Non-modulation time, L2 is tuned
to 10.7 MHZ, if modulation is applied and S] is changed
from 10.7 MHz, phase deviation at L2 will take place
proportionately in relation to this changed part and this
becomes 52 signal which is delayed in relation to SI.
s:—— —— —~
Fig. 11 Output at Non-modulation
Fig. 12 Output at Modulation Time
At Non-modulation, because at shown in Fig. ll, input
signal 81 and 90° phase delayed (by means of L1) signal
82 are switched by means of the multiplier circuit, the
output signal becomes S3.
Because this SB passes the low pass ﬁlter and becomes
S4 fixed direct current, the detector output is zero.
Then, when modulation is applied, because the switched
output is varied according to the degree of modulation,
and the output which passed the low pass ﬁlter becomes
the pulsating current part as shown in Fig. 12, detector
output is obtained.