ADA4891-3 Analog Devices, ADA4891-3 Datasheet - Page 15

• Manufacturer Part Number: ADA4891-3
• Description: Low Cost CMOS, High Speed, Rail-to-Rail Amplifier (Triple)
• Manufacturer: Analog Devices

Specifications of ADA4891-3

• -3db Bandwidth: 220MHz
• Slew Rate: 170V/µs
• Vos: 2.5mV
• Ib: 2pA
• # Opamps Per Pkg: 3
• Input Noise (nv/rthz): 9nV/rtHz
• Vcc-vee: 2.7V to 5.5V
• Isy Per Amplifier: 4.4mA
• Packages: Mini-SO,SOP

APPLICATIONS INFORMATION
USING THE ADA4891
Understanding the subtleties of the ADA4891 family of amplifiers
provides insight into how to extract the peak performance from
the device. The following sections describe the effect of gain,
component values, and parasitics on the performance of the
ADA4891. The wideband, noninverting gain configuration of
the ADA4891 is shown in Figure 50; the wideband, inverting
gain configuration of the ADA4891 is shown in Figure 51.
WIDEBAND, NONINVERTING GAIN OPERATION
In Figure 50, R
respectively. Together, R
amplifier. The value of R
more information, see the Effect of R
section). Typical R
ADA4891-1/ADA4891-2. Typical R
to 453 Ω for the ADA4891-3/ADA4891-4.
In a controlled impedance signal path, R
termination resistor designed to match the input source imped-
ance. Note that R
generally set to match the input source impedance.
Table 5. Recommended Component Values and Effect of Gain on ADA4891-1/ADA4891-2 Performance (R
Gain
−1
+1
+2
+5
+10
SOURCE
R
604
0
604
604
604
V
50Ω
F
I
Figure 50. Noninverting Gain Configuration
(Ω)
F
Feedback Network Values
and R
T
F
is not required for normal operation. R
values range from 549 Ω to 698 Ω for the
G
R
denote the feedback and gain resistors,
T
F
0.1µF
F
and R
R
defines the 0.1 dB bandwidth (for
G
ADA4891
R
604
Open
604
151
67.1
G
G
+V
–V
determine the noise gain of the
(Ω)
S
S
0.1µF
F
F
values range from 301 Ω
R
on 0.1 dB Gain Flatness
F
10µF
T
is used as the input
V
O
10µF
R
−3 dB Small-Signal Bandwidth (MHz)
V
118
240
120
32.5
12.7
L
OUT
= 200 mV p-p
T
is
Rev. C | Page 15 of 24
ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4
WIDEBAND, INVERTING GAIN OPERATION
Figure 51 shows the inverting gain configuration. For the
inverting gain configuration, set the parallel combination of
R
Note that a bias current cancellation resistor is not required in
the noninverting input of the amplifier because the input bias
current of the ADA4891 is very low (less than 2 pA). Therefore,
the dc errors caused by the bias current are negligible.
For both noninverting and inverting gain configurations, it is
often useful to increase the R
output. Increasing the R
the expense of reducing the 0.1 dB bandwidth of the amplifier.
This effect is discussed further in the Effect of R
Flatness section.
RECOMMENDED VALUES
Table 5 and Table 6 provide a quick reference for various configu-
rations and show the effect of gain on the −3 dB small-signal
bandwidth, slew rate, and peaking of the ADA4891-1/ADA4891-2/
ADA4891-3/ADA4891-4. Note that as the gain increases, the
small-signal bandwidth decreases, as is expected from the gain
bandwidth product relationship. In addition, the phase margin
improves with higher gains, and the amplifier becomes more
stable. As a result, the peaking in the frequency response is
reduced (see Figure 7 and Figure 10).
T
and R
G
SOURCE
to match the input source impedance.
V
50Ω
I
Figure 51. Inverting Gain Configuration
R
t
188
154
170
149
71
R
T
R
G
F
Slew Rate (V/μs)
value improves harmonic distortion at
F
ADA4891
value to decrease the load on the
+V
–V
t
192
263
210
154
72
F
S
S
0.1µF
0.1µF
L
R
= 1 kΩ)
F
V
O
F
10µF
10µF
on 0.1 dB Gain
Peaking (dB)
1.3
2.6
1.4
0
0
R
L