Datasheet

Inverting Gain Stage
3-3
EVM Applications
3.3 Inverting Gain Stage
If unity gain inverting operation is desired, the user should:
- Change R6 to 0 Ω
- Remove R7
- Change R4 to 0 Ω
- Change R2 to 57.6 Ω (R3 in parallel with R2 equals 50 Ω for termination
of the input)
as shown in Figure 3-3.
Figure 3-3. Inverting Gain Stage
R6
R2
R5
J4
Vout
J1
Vin-
Vs-
-
+
U1
2
3
6
7
4
R3
Vs+
R4
392 
392 
57.6 
0 
0 
The gain for this circuit with a 50-Ω source is:
V
O
V
I
+*
R5
R3
when the input voltage is measured at J1.
The input impedance of the stage is 50 Ω, as determined by R2 in parallel with
R3.
3.4 Power-Down Reference Operation—THS4215EVM Only
For the default EVM configuration, power-down reference level is set to
ground through R1. This reference can be set to a different level if R1 is
removed and an external voltage is supplied to J8 as shown in Figure 3-4.