TK14551V/14551 TOKO [TOKO, Inc], TK14551V/14551 Datasheet - Page 23

• Manufacturer Part Number: TK14551V/14551
• Description: FM IF DETECTOR/AMPLIFIER
• Manufacturer: TOKO [TOKO, Inc]

TK14551V
CIRCUIT DESCRIPTION
FM Detector:
The FM detector is included in the quadrature FM detector using a Gilbert multiplier.
It is suitable for high speed data communication because the demodulation bandwidth is over 1 MHz.
The phase shifter is connected between Pin 3 (IF limiter output) and Pin 4 (input detector). Any available phase shifter
can be used: a LC resonance circuit, a ceramic discriminator, a delay line, etc.
Figure 6 shows the internal equivalent circuit of the detector.
V CC
V CC
V CC
QB
QA
multiplier core circuit
FIGURE 6 - DETECTOR INTERNAL EQUIVALENT CIRCUIT
The signal from the phase shifter is applied to the multiplier (in the dotted line) through emitter-follower stage QA. When
the phase shifter is connected between pin 3 and pin 4, note that the bias voltage to pin 4 should be provided from an
external source because pin 4 is only connected to the base of QA.
Because the base of QB (at the opposite side) is connected with the supply voltage, Pin 4 has to be biased with the
equivalent voltage.
Using an LC resonance circuit is not a problem (see Figure 7). However, when using a ceramic discriminator, it is
necessary to pay attention to bias. If there is a difference of the base voltages, the DC voltages of the multiplier do not
balance. It alters the DC zero point or worsens the distortion of demodulation output.
The Pin 4 input level should be saturated at the multiplier; if this level is lower, it is easy to disperse the modulation output.
Therefore, to have stable operation, Pin 4 should be higher than 100 mV
.
P-P
The following figures show examples of the phase shifter.
Rz is the characteristic impedance
V CC
V CC
V CC
Rz
Rz
Delay
Line
LC resonance circuit
ceramic discriminator
delay line
FIGURE 7 - EXAMPLES OF PHASE SHIFTERS
January 2000 TOKO, Inc.
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