Texas Instruments THS4012 - Manual (Page 18)

THS4012 EVM Differential Input
1-12 General
Figure 1–5. THS4012 EVM Schematic — Differential Input (Inverting Operation)
C1
6.8 µ F
–VCC
1
GND
2
+VCC
3
J2
C2
6.8 µ F
–VCC
+VCC
–
+
U1:A
THS4012
1
4
8 2
3
R4
1 k Ω
R6
1 k Ω
+VCC
C3
x
µ
F
R7
49.9
Ω
Vout1
J3
C4
0.1
µ
F
–VCC
R2
0
Ω
J1
Vin1
R8
100
Ω
–
+
U1:B
THS4012
7
6
5
R12
1 k Ω
R14
1 k
Ω
C6
x
µ
F
R15
49.9 Ω
Vout2
J5
R10
0 Ω
J4
Vin2
C5
0.1 µ F
The gain of the EVM inputs can easily be changed to support a particular
application by changing the ratio of resistors R6 and R4 (channel 1) and R14
and R12 (channel 2) as described in the following equation:
Inverting Gain +
–R
F
R
G
+
–R6
R4
and –R14
R12
R4 and R12 form part of the input impedance and R8 should be adjusted in
accordance with the following equation:
R8
+
2 R4 R
T
R4–R
T
where R
T
is the termination resistance and R4 = R12.
In addition, some applications, such as those for video, may require the use
of 75-
Ω
cable and 75-
Ω
EVM input termination and output isolation resistors.