AD8004 Analog Devices, AD8004 Datasheet - Page 9

• Manufacturer Part Number: AD8004
• Manufacturer: Analog Devices

Specifications of AD8004

• -3db Bandwidth: 250MHz
• Slew Rate: 3kV/µs
• Vos: 1mV
• Ib: 35µA
• # Opamps Per Pkg: 4
• Input Noise (nv/rthz): 1.5nV/rtHz
• Vcc-vee: 4V to 12V
• Isy Per Amplifier: 4.25mA
• Packages: DIP,SOIC

THEORY OF OPERATION
The AD8004 is a member of a new family of high speed current-
feedback (CF) amplifiers offering new levels of bandwidth,
distortion, and signal-swing capability vs. power. Its wide dynamic
range capabilities are due to both a complementary high speed
bipolar process and a new design architecture. The AD8004 is
basically a two stage (Figure 30) rather than the conventional
one stage design. Both stages feature the current-on-demand
property associated with current feedback amplifiers. This
gives an unprecedented ratio of quiescent current to dynamic
performance. The important properties of slew rate and full
power bandwidth benefit from this performance. In addition
the second gain stage buffers the effects of load impedance,
significantly reducing distortion.
A full discussion of this new amplifier architecture is available on
the data sheet for the AD8011. This discussion only covers the
basic principles of operation.
DC AND AC CHARACTERISTICS
As with traditional op amp circuits the dc closed-loop gain is
defined as:
REV. C
A
A
V
V
= G = 1 +
= G = −
R
R
INP
IPP
R
R
N
F
V
N
P
F
Q1
Q2
noninverting operation
inverting operation
V
N
Q3
Q4
IQ1
IQ1
IPN
IPN
IE
A1
A1
Z
I
Figure 5. Simplified Block Diagram
C
C
P
1
P
1
C
–9–
A2
P
A2
C
C
2
D
D
Z2
The more exact relationships that take into account open-loop
gain errors are:
In these equations the open-loop voltage gain (A
to both voltage and current-feedback amplifiers and is the ratio
of output voltage to differential input voltage. The open-loop
transimpedance gain (T
inverting input current and is applicable to current-feedback
amplifiers. The open-loop voltage gain and open-loop transim-
pedance gain (T
in TPCs 15 and 18. These plots and the basic relationships can
be used to predict the first order performance of the AD8004 over
frequency. At low closed-loop gains the term (R
the frequency response characteristics. This gives the result that
bandwidth is constant with gain, a familiar property of current
feedback amplifiers.
An R
optimum frequency response with acceptable peaking at gains of
+2/–1. As can be seen from the above relationships, at higher
closed-loop gains reducing R
loop bandwidth. Table I gives optimum values for R
for a variety of gains.
ICQ +
V
A
A
F
O
AD8004
V
of 1 k has been chosen as the nominal value to give
´
V
=
=
IO
A3
1 +
1 +
A
1 − G
A
O
G
O
O
(s)
(s)) of the AD8004 are plotted vs. frequency
(s)
G
G
R
G
+
+
R
F
T
T
O
R
O
(s)) is the ratio of output voltage to
R
O
F
(s)
(s)
F
F
has the effect of increasing closed-
R
L
for inverting (G is negative)
for noninverting (G is positive)
C
L
V
O
F
/T
O
AD8004
(s)) is common
O
(s)) dominates
F
and R
G