MT8870 查看數據表（PDF） - Mitel Networks

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产品描述 (功能)

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MT8870

Integrated DTMF Receiver

Mitel Networks 

MT8870D/MT8870D-1 ISO2-CMOS

Applications

RECEIVER SYSTEM FOR BRITISH TELECOM

SPEC POR 1151

The circuit shown in Fig. 9 illustrates the use of

MT8870D-1 device in a typical receiver system. BT

Spec defines the input signals less than -34 dBm as

the non-operate level. This condition can be

attained by choosing a suitable values of R1 and R2

to provide 3 dB attenuation, such that -34 dBm input

signal will correspond to -37 dBm at the gain setting

pin GS of MT8870D-1. As shown in the diagram, the

component values of R3 and C2 are the guard time

requirements when the total component tolerance is

6%. For better performance, it is recommended to

use the non-symmetric guard time circuit in Fig. 8.

VDD

St/GT

R1

ESt

tGTP=(RPC1)In[VDD/(VDD-VTSt)]

tGTA=(R1C1)In(VDD/VTSt)

RP=(R1R2)/(R1+R2)

C1

R2

Notes:

R1=368K Ω ± 1%

R2=2.2M Ω ± 1%

C1=100nF ± 5%

Figure 8 - Non-Symmetric Guard Time Circuit

DTMF

Input

C1

R1

R2

X1

VDD

MT8870D-1

IN+

IN-

GS

VRef

INH

PWDN

OSC 1

OSC 2

VSS

VDD

St/GT

ESt

StD

Q4

Q3

Q2

Q1

TOE

C2

R3

NOTES:

R1 = 102KΩ ± 1%

R2 = 71.5KΩ ± 1%

R3 = 390KΩ ±1 %

C1,C2 = 100 nF ± 5%

X1 = 3.579545 MHz ± 0.1%

VDD = 5.0V ± 5%

Figure 9 - Single-Ended Input Configuration for BT or CEPT Spec

4-16

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