LMH6618MK NSC [National Semiconductor], LMH6618MK Datasheet - Page 21

• Manufacturer Part Number: LMH6618MK
• Description: 130 MHz, 1.25 mA Rail-to-Rail Input and Output Operational Amplifier with Shutdown
• Manufacturer: NSC [National Semiconductor]

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 6
can do both of these tasks. The procedure for specifying the
resistor values is as follows.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10. Calculate R
11. Calculate R
12. Calculate R
Check that both the V
ranges of the LMH6618.
The following example is for a V
2V to 4V.
1.
2.
3.
4.
5.
6.
Determine the input voltage.
Calculate the input voltage midpoint, V
(V
Determine the output voltage needed.
Calculate the output voltage midpoint, V
V
Calculate the gain needed, gain = (V
(V
Calculate the amount the voltage needs to be shifted
from input to output, ΔV
Set the supply voltage to be used.
Calculate the noise gain, noise gain = gain + ΔV
Set R
V
V
V
V
Gain = (4V – 2V)/(1V – 0V) = 2
ΔV
OUTMIN
IN
INMID
OUT
OUTMID
INMAX
INMAX
OUT
= 0V to 1V.
= 2V to 4V.
F
.
= 0V + (1V – 0V)/2 = 0.5V.
= 3V – 2 x 0.5V = 2.
– V
– V
+ (V
= 2V + (4V – 2V)/2 = 3V.
INMIN
INMIN
1
2
G
, R
, R
OUTMAX
, R
1
2
G
)/2.
)
= R
= R
= R
IN
– V
F
F
F
/gain.
/(noise gain-gain).
/(noise gain – 1).
and V
OUTMIN
OUT
IN
= V
OUT
of 0V to 1V with a V
)/2.
FIGURE 7. 4
OUTMID
are within the voltage
OUTMAX
– gain x V
INMID
OUTMID
th
= V
– V
Order Multiple Feedback Low-Pass Filter
=
INMIN
OUTMIN
OUT
INMID
OUT
/V
+
.
S
of
)/
.
21
7.
8.
9.
10. R
11. R
12. R
4
Figure 7 shows the LMH6618 used as the amplifier in a mul-
tiple feedback low-pass filter. This filter is set up to have a
gain of +1 and a −3 dB point of 1 MHz. Values can be deter-
mined by using the WEBENCH
at amplifiers.national.com.
th
ORDER MULTIPLE FEEDBACK LOW-PASS FILTER
For the example the supply voltage will be +5V.
Noise gain = 2 + 2/5V = 2.4.
R
F
1
2
G
= 2 kΩ
= 2 kΩ/2 = 1 kΩ
= 2 kΩ/(2.4-2) = 5 kΩ.
= 2 kΩ/(2.4 – 1) = 1.43 kΩ.
FIGURE 6. DC Level Shifting
®
Active Filter Designer found
20195828
20195848
www.national.com