LMV822MM National Semiconductor, LMV822MM Datasheet - Page 14

• Manufacturer Part Number: LMV822MM
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LMV822MM

• No. Of Amplifiers: 1
• Bandwidth: 5MHz
• Slew Rate: 1.4V/µs
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): No
• Single Supply Voltage Min (+v): 2.7V
• Input Offset Voltage Max: 3.5mV
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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the pass band gain. Increasing R
the gain by 0.4 dB, while increasing R
creased the gain by 0.4 dB.
Active filters are also sensitive to an op amp’s parameters
-Gain and Bandwidth, in particular. The LMV822/24 provide
a large gain and wide bandwidth. And DAAFs make excel-
lent use of these feature specifications.
Single Amplifier versions require a large open-loop to
closed-loop gain ratio - approximately 50 to 1, at the Fc of
the filter response. Figure 12 shows an impressive photo-
graph of a network analyzer measurement (hp3577A). The
measurement was taken from a 300kHz version of Figure
10 . At 300 kHz, the open-loop to closed-loop gain ratio
is about 5 to 1. This is 10 times lower than the 50 to 1 “rule
of thumb” for Single Amplifier Active Filters.
In addition to performance, DAAFs are relatively easy to de-
sign and implement. The design equations for the low-pass
and high-pass DAAFs are shown below. The first two equa-
tion calculate the Fc and the circuit Quality Factor (Q) for the
LPF ( Figure 10 ). The second two equations calculate the Fc
and Q for the HPF ( Figure 11 ).
Component (LPF)
R
C
R
R
C
R
R
a
1
2
3
3
4
5
FIGURE 12. 300 kHz, Low-Pass Filter, Butterworth
Response as Measured by the HP3577A Network
Sensitivity (LPF)
-1.2
-0.1
-1.1
+0.7
-1.5
-0.6
+0.6
Analyzer
4
by ten percent, increased
5
by ten percent, de-
DS100128-92
Component (HPF)
C
R
R
C
R
R
R
a
b
1
2
3
4
5
@
Fc
TABLE 1.
14
To simplify the design process, certain components are set
equal to each other. Refer to Figure 10 and Figure 11 . These
equal component values help to simplify the design equa-
tions as follows:
To illustrate the design process/implementation, a 3 kHz,
Butterworth response, low-pass filter DAAF ( Figure 10 ) is
designed as follows:
1. Choose C
2. Choose R
3. Calculate R
4. Calculate R
worth (Maximally Flat) response is 0.707 (45 degrees into
the s-plane). R
Notice that R
The circuit was implemented and its cutoff frequency mea-
sured. The cutoff frequency measured at 2.92 kHz.
The circuit also showed good repeatability. Ten different
LMV822 samples were placed in the circuit. The correspond-
ing change in the cutoff frequency was less than a percent.
Sensitivity (HPF)
-0.7
-1.0
+0.1
-0.1
+0.1
-0.1
+0.1
1
4
3
3
= C
= R
a
could also be calculated as 0.707 of R
3
for the desired Q. The desired Q for a Butter-
and R
calculates as follows:
3
5
= C = 1 nF
= 1 k
2
for the desired Fc as follows:
a
or R
2.