MT8870D/MT8870D-1 ISO2-CMOS
Applications
RECEIVER SYSTEM FOR BRITISH TELECOM
SPEC POR 1151
t
=(R C )In[V /(V -V )]
GTP
P
1
DD
DD TSt
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 R and R to
t
=(R C )In(V /V
)
GTA
1
1
DD TSt
R =(R R )/(R +R )
V
P
1
2
1
2
DD
C
1
2
1
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
St/GT
ESt
component values of R and C are the guard time
3
2
R
R
1
2
Notes:
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.
R =368K Ω 1%
1
R =2.2M Ω 1%
2
C =100nF 5%
1
Figure 8 - Non-Symmetric Guard Time Circuit
V
DD
C
1
DTMF
Input
C
2
MT8870D-1
R
1
V
IN+
DD
IN-
GS
V
St/GT
ESt
StD
Q4
R
3
R
2
Ref
INH
Q3
PWDN
OSC 1
OSC 2
Q2
NOTES:
X
1
R = 102KΩ 1%
Q1
1
R = 71.5KΩ 1%
2
TOE
V
SS
R = 390KΩ 1 %
3
C ,C = 100 nF 5%
1
2
X = 3.579545 MHz 0.1%
1
V
= 5.0V 5%
DD
Figure 9 - Single-Ended Input Configuration for BT or CEPT Spec
4-16
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
