MX105AP datasheet(8/15 Pages) CMLMICRO

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Tone Detector

MX105A PRELIMINARY INFORMATION

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5.5 Select R4 for Operating BW

4.8 BW

10.35 BW

4.8

10.35

6.8k

−

≈Ω

The exact bandwidth given by any value of R4 will vary slightly. In applications where an exact bandwidth is required, R4

should be a variable resistor to permit adjustment.

5.6 Calculate R2

×C2A

100

×≈

××

For a frequency of 2800 Hz, a bandwidth of 6%, and a choice of C2

0.01 F

200k

=⇒

µΩ .

Note: Use nearest preferred values.

5.7 Define Maximum Allowed Response Time

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

The MX105A’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

150

fBW

LOCK

Using the formula above, for a frequency of 2800 Hz and a bandwidth of 6% the approximate Lock time (TLOCK) will be 9

ms. Since the maximum response time is 50 ms, a DETECT time of 41 ms is allowed.

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

B. Calculate Maximum Allowable TDETECT

DETECT

LOCK

MAX

=−

C. Define Minimum Expected Signal Amplitude

()

VIN

MIN

This is used in calculating TDETECT components.

5.8 Calculate R3

×C3A

3ln 1

DETECT

MIN

×≈

−×

−













where: VTH is the detect filter sensitivity.

Note:

For a signal amplitude of 200 mVRMS, a resistor value R3 of 510 kΩ with a 0.1µF capacitor for C3A and C3B will yield

a TDETECT time of 20ms. This in turn yields a response time of 9ms + 20 ms = 29ms.

Use nearest preferred values.

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