Datasheet
NONINVERTING AMPLIFIER WITH REDUCED SINGLE-SUPPLY ACTIVE FILTER
1/2
OPA2830
V
OUT
+5V
V
IN
R
G
R
T
R
F
R
C
G
1
+ 1 )
R
F
R
G
G
2
+ 1 )
R
T
)
R
F
G
1
R
C
NG + G
1
G
2
1/2
OPA2830
1.5k
Ω
1.87k
Ω
500
Ω
+5V
1.87k
Ω
4V
I
V
I
150pF
0.1
µ
F
1MHz, 2nd−Order
Butterworth Filter
100pF
432
Ω
137
Ω
0.1
µ
F
OPA2830
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.................................................................................................................................................. SBOS309D – AUGUST 2004 – REVISED AUGUST 2008
PEAKING
The OPA2830 operating on a single +3V or +5V
Figure 77 shows a noninverting amplifier that reduces supply lends itself well to high-frequency active filter
peaking at low gains. The resistor R
C
compensates designs. The key additional requirement is to
the OPA2830 to have higher Noise Gain (NG), which establish the DC operating point of the signal near
reduces the AC response peaking (typically 4dB at the supply midpoint for highest dynamic range.
G = +1 without R
C
) without changing the DC gain. V
IN
Figure 78 shows an example design of a 1MHz
needs to be a low impedance source, such as an op low-pass Butterworth filter using the Sallen-Key
amp. topology.
Both the input signal and the gain setting resistor are
AC-coupled using 0.1 µ F blocking capacitors (actually
giving bandpass response with the low-frequency
pole set to 32kHz for the component values shown).
This allows the midpoint bias formed by the two
1.87k Ω resistors to appear at both the input and
output pins. The midband signal gain is set to +4
(12dB) in this case. The capacitor to ground on the
noninverting input is intentionally designed at a higher
value to dominate input parasitic terms. At a gain of
+4, the OPA2830 on a single supply will show 30MHz
small- and large-signal bandwidth. The filter resistor
values have been slightly adjusted to account for this
Figure 77. Compensated Noninverting Amplifier
limited bandwidth in the amplifier stage. Tests of this
circuit show a precise 1MHz, – 3dB point with a
The Noise Gain can be calculated as follows:
maximally-flat passband (above the 32kHz
AC-coupling corner), and a maximum stop band
attenuation of 36dB at the amplifier's – 3dB bandwidth
of 30MHz.
A unity-gain buffer can be designed by selecting
R
T
= R
F
= 20.0 Ω and R
C
= 40.2 Ω (do not use R
G
).
This gives a noise gain of 2, so the response will be
similar to the Characteristics Plots with G = +2 giving
less peaking.
Figure 78. Single-Supply, High-Frequency Active Filter
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