MX105ALH 查看數據表（PDF） - MX-COM Inc

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MX105ALH

Tone Detector

MX-COM Inc  

Tone Detector

10

MX105A PRELIMINARY INFORMATION

5.10 Calculate Signal to Noise Performance

Worst-case S/N calculations depend on calculation of a value “M” using the formula shown below:

M = R3 × C3A

3 × R2 × C2A

substituting example values,

M = 510 × 0.1 = 8.5

3 × 200 × 0.01

By substituting this value for M in Figure 5, the minimum required S/N of an in band tone with respect to an adjacent

interfering tone can be found. This then has to be increased depending on the input tone amplitude.

-28

M =∞

-24

M=1

-20

M = 0.33

-16

M = 0.1

-12

-8

-4

0

12 4

6

8 10

Number of Bandwidths Separation

Figure 5: S/N vs. BW Separation

The following formula expresses the reduction in noise immunity as the input signal approaches the detect filter sensitivity

VTH.

required S

N

=



20log



VIN

VIN − VTH







+

S

N Figure 5

If this S/N is better than required for the application, R3×C3A can be reduced, or the operating bandwidth can be

increased to obtain a faster tone detection time.

If the S/N performance is not adequate, the operating bandwidth can be reduced toward the MUBW, or R3C3A can be

increased to improve S/N performance at the expense of slower response time.

5.11 Calculate C4 for 30° Phase Shift

Capacitor C4 is used to phase shift the input to the VCO commutating filter by 30°, thereby shifting the sampling clocks by

the same amount. This enables the Detect sampling filter to sample and integrate at the maximum and minimum of the

input tone.

C4 = tan(30° ) ≈ 0.092 ≈ 164pF

2π ×f0 × RV f0× RV

© 1997 MX•COM, INC.

www.mxcom.com Tele: 800 638 5577 910 744 5050 Fax: 910 744 5054

Doc.# 20480133.003

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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