Noninverting Gain Stages
3-2
Figure 3-2. AC-Coupled, Single Power Supply, Noninverting Gain Stage
R8
1 k
Ω
R6
Z1
Z2
J7
Vref
J2
Vin+
-
+
U1
THS4601
2
3
6
7
4
J3
Vout
TP3
Vout
R1
0
VS+
Z3
VS+
R5
Z5
100
Ω
R7
R2
49.9
Ω
R3
100
Ω
*Power supply decoupling is not shown
Ω
Z1 through Z3 are populated with dc-blocking capacitors, selected so they do
not interfere with the frequencies that are of interest. These capacitors create
high pass characteristics. R5 through R7 are selected to produce a dc
potential on the noninverting input equal, or close to VS+ divided by 2. The
THS4601 has low input bias currents, which allow larger bias setting resistors.
If the user prefers, an external potential can be introduced at J7—use only R7
and R5. If the source of VS+ in the system is noisy, and there is a less noisy
potential available in the system, it can be connected to J7. R7 and R5 can then
be used as a voltage divider off of the reference attached to J7 to create the
VS+ divided by 2 potential.
The gain measured from J2 to J3 is 2, and is still determined by:
Vout
V
in
)
+
1
)
Z5
R3
(in the passband of the stage).