OPA2830_08 Datasheet, PDF (26/41 Pages) Burr-Brown (TI) – Dual, Low-Power, Single-Supply, Wideband OPERATIONAL AMPLIFIER

OPA2830
SBOS309C – AUGUST 2004 – REVISED MARCH 2006
NONINVERTING AMPLIFIER WITH REDUCED
PEAKING
Figure 77 shows a noninverting amplifier that
reduces peaking at low gains. The resistor R_C
compensates the OPA2830 to have higher Noise
Gain (NG), which reduces the AC response peaking
(typically
4dB
at
G = +1 without R_C) without changing the DC gain.
V_IN needs to be a low impedance source, such as an
op amp.
R_T
V_IN
+5V
1/2
R_{C OPA2830}
V_OUT
R_G
R_F
Figure 77. Compensated Noninverting Amplifier
The Noise Gain can be calculated as follows:
G₁
+
1
)
R_F
R_G
G₂
+
1
)
R_T )
R_C
RF
G1
NG + G₁ G₂
A unity-gain buffer can be designed by selecting
www.ti.com
R_T = R_F = 20.0Ω and R_C = 40.2Ω (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.
SINGLE-SUPPLY ACTIVE FILTER
The OPA2830 operating on a single +3V or +5V
supply lends itself well to high-frequency active filter
designs. The key additional requirement is to
establish the DC operating point of the signal near
the supply midpoint for highest dynamic range.
Figure 78 shows an example design of a 1MHz
low-pass Butterworth filter using the Sallen-Key
topology.
Both the input signal and the gain setting resistor are
AC-coupled using 0.1µF 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
1.87kΩ 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 limited bandwidth in the amplifier
stage. Tests of this circuit show a precise 1MHz,
–3dB point with a 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.
0.1µF
V_I
1.87kΩ
137Ω
1.87kΩ
+5V
100pF
432Ω
1/2
150pF OPA2830
1.5kΩ
4V_I
1MHz, 2nd−Order
Butterworth Filter
500Ω
0.1µF
Figure 78. Single-Supply, High-Frequency Active Filter
26
Submit Documentation Feedback