FX105A Datasheet, PDF (8/16 Pages) CML Microcircuits – Tone Detector

Tone Detector
FX105A
1.6.2.2 Calculate Minimum Usable Bandwidth (%)
Minimum Usable Bandwidth (MUBW) is the TOTAL (%) bandwidth required for the following:
(a) Input signal frequency tolerance (∆f₀)
(b) FX105A VCO temperature coefficient (T_C = −100ppm/ºC)
(c) FX105A VCO supply voltage coefficient (V_C = 2330ppm/V)
Add (a), (b) and (c) and express as TOTAL (%) bandwidth, not as a ± (%) value.
MUBW = Df₀ + |T_c|DTEMP + V_cDV_DD
MUBW = 0.5 + 0.01 x 100 + 0.233 x 1 » 2%
1.6.2.3 Calculate the Recommended Operating Bandwidth
Note again that this is the TOTAL (%) bandwidth:
BW = ½ [10 + MUBW] = ½ (10 + 2) = 6%
1.6.2.4 Select R₂ for Operating BW
R₂ = 4.8 BW/ [10.35 -BW] = 4.8 x 6/ (10.35 -6) » 6.8kW
The exact bandwidth given by any value of R₂ will vary slightly. In applications where an exact
bandwidth is required, R₂ should be a variable resistor to permit adjustment.
1.6.2.5 Calculate R_VC_2A (C_2A = C_2B) Use nearest preferred values
R_VC_2A » 100/ [3 f₀ BW] » 100/ (3 x 2800 x 6) » 2msec
Therefore
R_V » 200kW for C_2A = C_2B = 10nF
1.6.2.6 Define the Maximum Allowed Response Time
The maximum response time (T_ON) is the sum of the VCO lock time (T_LOCK) and the Word integration
time (T_WORD). The FX105A’s T_ON must not exceed the maximum time allowed for the application, but
a value lying near the maximum gives the best S/N performance.
(a) Calculate T_LOCK
T_LOCK = 150/ [f₀ BW] = 150/ (2800 x 6) » 9msec
Note: T_LOCK may vary from near zero to the value given, causing corresponding variations in actual
T_ON.
(b) Calculate Maximum Allowable T_WORD
T_WORD = T_ONMAX -T_LOCK = 50 - 9 = 41msec
Note: Since the maximum allowed response time (T_ON) is 50msec, a maximum Word integration time
of 41msec is available.
© 1999 Consumer Microcircuits Limited
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D/105A/5