DSB75 Development Support Board Rev. B1 Hardware Description
Confidential / Released
DSB75_hd_v12
Page 55 of 96
2008-08-26
3.12 Analog
Interface
The DSB75 provides an analog interface allowing you to efficiently evaluate the
characteristics of the analog baseband codec of the GSM module:
•
This analog interface has 2 analog inputs and one analog output.
•
The analog input lines are available on the pin header X101.
•
The analog output is available as a pulse width modulation (PWM) signal on the pin
header X101.
•
A filter circuit 2
nd
order smoothes the PWM signal.
•
The filter on the DSB75 is optimized for 8.125kHz PWM frequency and can be removed
by customer. Therefore the jumpers X560 - X562 have to be replaced by customer
circuit.
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0,1
1
10
100
1000
10000
100000
PWM frequency [Hz]
Fi
lt
e
r a
tt
e
nua
ti
on [
d
B
]
Figure 29 PWM filter characteristics
•
For self test facilities it is possible to turn on test loops. Each analog input can be
connected to the filter output.
Figure 30 shows the placement of the related switches and the pin location.
Figure 31 shows the simplified interface schematic.
Electrical characteristics are specified in section 8.
X5
11
X5
51
X5
52
X101
X102
S201
S200
X554
X703
X561
X560
X562
S5
04
S5
03
S5
02
S5
01
S5
00
1
10
39
40
1
2
39
40
1
2
1
1
1
9 10
2
9
1
3
Figure 30: Analog interface location and related switches
