FX105AP3 datasheet(8/16 Pages) CMLMICRO

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Tone Detector

FX105A

D/105A/5

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 (TC = −100ppm/ºC)

(c)

FX105A VCO supply voltage coefficient (VC = 2330ppm/V)

Add (a), (b) and (c) and express as TOTAL (%) bandwidth, not as a ± (%) value.

MUBW = Df0 + |Tc|DTEMP + VcDVDD

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 RVC2A (C2A = C2B) Use nearest preferred values

RVC2A » 100/ [3 f0 BW] » 100/ (3 x 2800 x 6) » 2msec

Therefore

RV » 200kW for C2A = C2B = 10nF

1.6.2.6 Define the Maximum Allowed Response Time

The maximum response time (TON) is the sum of the VCO lock time (TLOCK) and the Word integration

time (TWORD). The FX105A’s TON 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 TLOCK

TLOCK = 150/ [f0 BW] = 150/ (2800 x 6) » 9msec

Note: TLOCK may vary from near zero to the value given, causing corresponding variations in actual

TON.

(b)

Calculate Maximum Allowable TWORD

TWORD = TON

MAX

-TLOCK = 50 - 9 = 41msec

Note: Since the maximum allowed response time (TON) is 50msec, a maximum Word integration time

of 41msec is available.

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