Datasheet
LMH6619
0.1 PF
10 PF
0.1 PF
V
+
1.24 k:
1 nF
150 pF
549:
V
+
-
+
22:
390 pF
14.3 k:
5.6 PF
14.3 k:
1 PF 549:
ADC121S705
0.1 PF
10 PF
V
+
LMH6619
0.1 PF
10 PF
0.1 PF
V
+
1.24 k:
1 nF
150 pF
549:
V
+
-
+
14.3 k:
5.6 PF
14.3 k:
1 PF 549:
22:
390 pF
+IN
-IN
LMH6618, LMH6619
www.ti.com
SNOSAV7E –AUGUST 2007–REVISED OCTOBER 2012
Figure 67. LMH6619 Driving an ADC121S705
DC LEVEL SHIFTING
Often a signal must be both amplified and level shifted while using a single supply for the op amp. The circuit in
Figure 68 can do both of these tasks. The procedure for specifying the resistor values is as follows.
1. Determine the input voltage.
2. Calculate the input voltage midpoint, V
INMID
= V
INMIN
+ (V
INMAX
– V
INMIN
)/2.
3. Determine the output voltage needed.
4. Calculate the output voltage midpoint, V
OUTMID
= V
OUTMIN
+ (V
OUTMAX
– V
OUTMIN
)/2.
5. Calculate the gain needed, gain = (V
OUTMAX
– V
OUTMIN
)/(V
INMAX
– V
INMIN
)
6. Calculate the amount the voltage needs to be shifted from input to output, ΔV
OUT
= V
OUTMID
– gain x V
INMID
.
7. Set the supply voltage to be used.
8. Calculate the noise gain, noise gain = gain + ΔV
OUT
/V
S
.
9. Set R
F
.
10. Calculate R
1
, R
1
= R
F
/gain.
11. Calculate R
2
, R
2
= R
F
/(noise gain-gain).
12. Calculate R
G
, R
G
= R
F
/(noise gain – 1).
Check that both the V
IN
and V
OUT
are within the voltage ranges of the LMH6618.
The following example is for a V
IN
of 0V to 1V with a V
OUT
of 2V to 4V.
1. V
IN
= 0V to 1V
2. V
INMID
= 0V + (1V – 0V)/2 = 0.5V
3. V
OUT
= 2V to 4V
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