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280
Bandpass Signaling Principles and Circuits Chap. 4
Tuned circuit
Envelope
detector
Tuned circuit #2
characteristic
Tuned circuit #1
characteristic
v 1 (t)
0
#1 @ f 1
Tuned circuit #1
f 2 f c f 1
Overall frequency-tovoltage
characteristic
+
–
v out (t)
0
f
Tuned circuit
Envelope
#2 @ f 2 detector
(a) Block Diagram
L 1 C 1
v 1 (t)
v out (t)
L 2 C 2
(b) Circuit Diagram
Tuned circuit #2
Figure 4–17
Balanced discriminator.
where the sum-frequency term is eliminated by the low-pass filter. For K 2 sufficiently small,
sin x ≈ x, and by the use of Eq. (4–83), the output becomes
v out (t) = 1 2 K 1K 2 V L 2 K f m(t)
(4–90)