TSH80I ST Microelectronics, Inc., TSH80I Datasheet - Page 16

• Manufacturer Part Number: TSH80I
• Description: Wide Band Rail to Rail Operational Amplifier With Standby Function
• Manufacturer: ST Microelectronics, Inc.

TSH80-TSH81-TSH82
Example of a video application:
This example shows a possible application of the TSH8X circuit. Here, you can multiplex the channels for
the different standard PAL, NTSC as you filter for the different bands; the video signal can be filtered with
two different cutoff frequencies, corresponding to a PAL encoded signal (LPF1) or a NTSC signal (LPF2).
You can multiplex input signals, as the outputs are in high impedance state in standby mode. This enables
you, to use a PAL filter as the Standby mode is active and to use the NTSC filter otherwise.
The video application requires 1Vpeak at input and output.
Calculation of components:
A decoupling capacitor is provided to cutoff the frequencies below 10Hz according I bias. Hence
Ce=10uF, with Rb1=10k . At the output, Cout=220uF.
The AOP1 is in 6dB configuration for the adaptation bridge. R1=R2=1k V1=2Vpk, V2=1Vpk
For the PAL communication, we need a low pass filtering. The load resistance R4 is function of the output
resistance of the filter.V3=V2/A1 where A1 is the attenuation factor of the filter LPF1.
To compensate the filter insertion loss, we add an additional factor to the gain of the 2nd amplifier AOP2.
For example, for an attenuation of 3dB, we choose R5=300
Vout=1Vpk.
The calculation of the parameters R7, C7, R8, C8, R9, R10 will be exactly the same.
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IN
Re
Phase Margin
Phase Margin
Phase Margin
Phase Margin
Parameter
f-3dB
f-3dB
f-3dB
f-3dB
Ce
Vcc/2
Vcc/2
Rb1
R1
+
-
AOP1
R2
Cf
Cf (pF)
V1
5.6
22
33
0
R3 C3
R7 C7
V2
Vcc=±1.5V
33.7
LPF1
LPF2
28
40
30
40
37
37
48
NTSC
A2
A1
PAL
V3
R4
R8
C4
C8
Vcc/2
Vcc/2
Vcc/2
Vcc/2
Vcc=±2.5V
Rb1
Rb1
39.3
39.3
30.7
R5
R9
43
43
52
34
65
and R6=1k . We have V4=2Vpk and
+
-
+
-
AOP2
Standby
Standby
AOP3
R6
Cf
R10
Cf
Vcc=±5V
V4
38.3
38.3
27.6
Rout
56
56
67
32
78
Cout
OUT
MHz
MHz
MHz
MHz
RL
Unit
deg
deg
deg
deg