FX105A Datasheet, PDF (9/16 Pages) CML Microcircuits – Tone Detector

Tone Detector
FX105A
1.6.2.7 Calculate R_WC_3A (C_3A = C_3B) Use nearest preferred values.
R_WC_3A » T_WORD/ [-3In (1 - V_TH/ V_INMIN ) ]
where V_TH is the word filter
sensitivity, see Section 1.7.1
A signal amplitude of 200mV and a resistor value R_W of 465kΩ with a 220nF capacitor for C_3A and
C_3B will yield a T_WORD time of 41msec. This in turn yields a response time of 9msec + 41msec =
50msec.
1.6.2.8 Calculate the Maximum De-response Time
T_OFF » -3 R_WC_3A In (V_TH/ V_INMAX )
where V_TH is the word filter
sensitivity, see Section 1.7.1
For improved de-response time, a diode (1N914 or similar) can be placed between pins 5 and 6, as
shown in Figure 2. The formula and figure below show the approximate time the FX105A will take to
turn off after an in-band signal has been removed. The effect of this diode is to greatly reduce the
turn-off time with signal input amplitudes greater than 300mV_rms. Figure 4 is for V_DD = 5V; for lower
V_DD then K_DT increases.
T_OFF » K_DTR_WC_3A
So for a maximum signal amplitude of 400mV, a resistor value R_W of 465kΩ with a 220nF capacitor
for C_3A and C_3B and a diode between pins 5 and 6, a de-response time of ≈ 363msec is obtained.
Figure 4 K_DT Factor for T_OFF vs. Signal Input Amplitude
© 1999 Consumer Microcircuits Limited
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