Tone Detector
FX105A
1.6.2.10 Calculation of PLL Filter Phase Shift
Capacitor C4 is used to phase shift the input to the VCO commutating filter by 30°, thus shifting the
sampling clocks by the same amount. This enables the "Word" sampling filter to sample and integrate
at the maxima and minima of the input tone.
C4 = tan (30°) / [2p f0 RV] » 0.092 / [f0 RV] » 164pF
1.6.3
Replacement for FX105
Figure 6 depicts the circuit changes required to replace a FX105 with a FX105A device. A 5V zener
diode and a resistor can be used to generate a 5V supply voltage from an existing 12V supply. If the
Detect Output needs to pull up beyond the 5V supply, a transistor amplifier following the output can
be used.
Figure 6 Circuit changes for 12V to 5V conversion
ã 1999 Consumer Microcircuits Limited
11
D/105A/5
CMLMICRO [ CML MICROCIRCUITS ]
