MT8870 Mitel Networks Corporation, MT8870 Datasheet - Page 6

• Manufacturer Part Number: MT8870
• Description: ISO2-CMOS Integrated DTMF Receiver
• Manufacturer: Mitel Networks Corporation

MT8870D/MT8870D-1
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.
attained by choosing a suitable values of R
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 R
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.
4-16
DTMF
Input
C
Figure 9 - Single-Ended Input Configuration for BT or CEPT Spec
1
3
and C
X
1
This condition can be
R
R
1
2
2
are the guard time
IN+
IN-
GS
V
INH
PWDN
OSC 1
OSC 2
V
MT8870D-1
Ref
SS
V
ISO
DD
1
and R
St/GT
2
TOE
V
-CMOS
StD
ESt
Q4
Q3
Q2
Q1
DD
2
Figure 8 - Non-Symmetric Guard Time Circuit
V
St/GT
ESt
DD
R
C
3
2
R
1
NOTES:
R
R
R
C
X
V
t
1
DD
GTP
1
2
3
1
,C
= 3.579545 MHz
= 102K
= 71.5K
= 390K
C
R
= 5.0V
2
=(R
1
2
= 100 nF
t
GTA
P
C
=(R
1
)In[V
R
5%
1 %
1%
P
1
1%
C
=(R
Notes:
R
R
C
DD
1
5%
)In(V
1
2
1
1
=368K
=2.2M
=100nF
/(V
R
0.1%
2
DD
)/(R
DD
-V
/V
1
TSt
+R
TSt
5%
)]
1%
)
2
1%
)