AD8067(Rev0) Ver la hoja de datos (PDF) - Analog Devices
Número de pieza
componentes Descripción
Fabricante
AD8067 Datasheet PDF : 24 Pages
| |||
THEORY OF OPERATION
The AD8067 is a low noise, wideband, voltage feedback operational
amplifier that combines a precision JFET input stage with Analog
Devices’ dielectrically isolated eXtra Fast Complementary Bipolar
(XFCB) process BJTs. Operating supply voltages range from 5 V
to 24 V. The amplifier features a patented rail-to-rail output stage
capable of driving within 0.25 V of either power supply while
sourcing or sinking 30 mA. The JFET input, composed of
N-channel devices, has a common-mode input range that includes
the negative supply rail and extends to 3 V below the positive
supply. In addition, the potential for phase reversal behavior has
been eliminated for all input voltages within the power supplies.
The combination of low noise, dc precision, and high bandwidth
makes the AD8067 uniquely suited for wideband, very high input
impedance, high gain buffer applications. It will also prove useful
in wideband transimpedance applications, such as a photodiode
interface, that require very low input currents and dc precision.
Basic Frequency Response
The AD8067’s typical open-loop response (see Figure 41) shows a
phase margin of 60° at a gain of +10. Typical configurations for
noninverting and inverting voltage gain applications are shown in
Figure 40 and Figure 42.
The closed-loop frequency response of a basic noninverting gain
configuration can be approximated using the equation:
Closed
Loop
–
3
dB
Frequency
=
(GBP ) ×
(RF
RG
+ RG
)
DC Gain = RF /RG + 1
GBP is the gain bandwidth product of the amplifier. Typical GBP
for the AD8067 is 300 MHz. See Table 1 for recommended values
of RG and RF.
Noninverting Configuration Noise Gain = RF +1
RG
RS RX
VI
SIGNAL
SOURCE
+VS
0.1µF
+
AD8067
–
0.1µF
–VS
+
10µF
RLOAD
10µF
+
+
VOUT
–
RF
RG FOR BEST PERFORMANCE,
SET RS + RX = RG || RF
Figure 40. Noninverting Gain Configuration
AD8067
90
120
80
90
70
60
PHASE
60
30
50
0
40
–30
GAIN
30
–60
20
–90
10
–120
0
–150
–10
0.01
0.1
1
10
100
FREQUENCY – MHz
Figure 41. Open-Loop Frequency Response
–180
1k
The bandwidth formula only holds true when the phase margin of
the application approaches 90°, which it will in high gain config-
urations. The bandwidth of the AD8067 used in a G = +10 buffer
is 54 MHz, considerably faster than the 30 MHz predicted by the
closed loop –3 dB frequency equation. This extended bandwidth is
due to the phase margin being at 60° instead of 90°. Gains lower
than +10 will show an increased amount of peaking, as shown in
Figure 4. For gains lower than +7, use the AD8065, a unity gain
stable JFET input op amp with a unity gain bandwidth of 145 MHz,
or refer to the Applications section for using the AD8067 in a gain
of 2 configuration.
Gain
10
20
50
100
RG (Ω)
110
49.9
20
10
RF (kΩ)
1
1
1
1
BW (MHz)
54
15
6
3
Table 1. Recommended Values of RG and RF
RX
RS
RG
+VS
0.1µF
+
10µF
+
AD8067
–
0.1µF
–VS
RLOAD
10µF
+
+
VOUT
–
VI
RF
SIGNAL
SOURCE
FOR BEST PERFORMANCE, SET RX = (RS + RG) || RF
Figure 42. Inverting Gain Configuration
Rev. 0 | Page 15 of 24
Share Link: 