AD813 Analog Devices, AD813 Datasheet - Page 13

• Manufacturer Part Number: AD813
• Description: Single Supply, Low Power Triple Video Amplifier
• Manufacturer: Analog Devices

Specifications of AD813

• -3db Bandwidth: 100MHz
• Slew Rate: 250V/µs
• Vos: 2mV
• Ib: 500nA
• # Opamps Per Pkg: 3
• Input Noise (nv/rthz): 3.5nV/rtHz
• Vcc-vee: 2.4V to 36V
• Isy Per Amplifier: 5.5mA
• Packages: DIP,LCC,SOIC

REV. B
General Consideration
The AD813 is a wide bandwidth, triple video amplifier that
offers a high level of performance on less than 5.5 mA per am-
plifier of quiescent supply current. With its fast acting power
down switch, it is designed to offer outstanding functionality
and performance at closed-loop inverting or noninverting gains
of one or greater.
Built on a low cost, complementary bipolar process, and achiev-
ing bandwidth in excess of 100 MHz, differential gain and phase
errors of better than 0.1% and 0.1 (into 150 ), and output
current greater than 40 mA, the AD813 is an exceptionally
efficient video amplifier. Using a conventional current feedback
architecture, its high performance is achieved through careful
attention to design details.
Choice of Feedback & Gain Resistors
Because it is a current feedback amplifier, the closed-loop band-
width of the AD813 depends on the value of the feedback resis-
tor. The bandwidth also depends on the supply voltage. In
addition, attenuation of the open-loop response when driving
load resistors less than about 250
width. Table I contains data showing typical bandwidths at
different supply voltages for some useful closed-loop gains when
driving a load of 150 . (Bandwidths will be about 20% greater
for load resistances above a few hundred ohms.)
V
+5
+3
The choice of feedback resistor is not critical unless it is impor-
tant to maintain the widest, flattest frequency response. The
resistors recommended in the table are those (metal film values)
that will result in the widest 0.1 dB bandwidth. In those appli-
cations where the best control of the bandwidth is desired, 1%
metal film resistors are adequate. Wider bandwidths can be
attained by reducing the magnitude of the feedback resistor (at
the expense of increased peaking), while peaking can be reduced
by increasing the magnitude of the feedback resistor.
15
5
S
(V)
Table I. –3 dB Bandwidth vs. Closed-Loop Gain and
Feedback Resistor , (R
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
Gain
L
= 150
R
866
681
357
681
357
750
649
154
649
154
715
619
154
619
154
681
619
154
619
154
F
( )
will also affect the band-
)
75
125
100
60
100
55
65
40
70
40
60
50
30
50
30
50
40
25
40
20
BW (MHz)
–13–
As discussed in many amplifier and electronics textbooks (such
as Roberge’s Operational Amplifiers: Theory and Practice), the
–3 dB bandwidth for the 2-pole model can be obtained as:
where:
and:
This model will predict –3 dB bandwidth within about 10% to
15% of the correct value when the load is 150 . However, it is
not accurate enough to predict either the phase behavior or the
frequency response peaking of the AD813.
+5
+3
To estimate the –3 dB bandwidth for closed-loop gains or feed-
back resistors not listed in the above table, the following two
pole model for the AD813 may be used:
where:
Appropriate values for the model parameters at different supply
voltages are listed in Table II. Reasonable approximations for
these values at supply voltages not found in the table can be
obtained by a simple linear interpolation between those tabu-
lated values which ‘bracket’ the desired condition.
V
15
5
S
Table II. Two Pole Model Parameters at Various Supplies
f 3
(V)
f n 1 2d
A
G = 1 + R
r
C
R
R
f
s
2
IN
A
CL
T
F
G
CL
= closed-loop gain from “transcapacitance”
= input resistance of the inverting input
= “transcapacitance,” which forms the
= feedback resistor
= gain resistor
= frequency of second (nondominant) pole
= 2 j f
r
85
90
105
115
S
open-loop dominant pole with the
transresistance
IN
2
( )
2
d
f n
(
R
F
(2 4d
F
1
2
2
/R
Gr
( R
G
f 2 (R
F
IN
f
2
2
)
C
F
Gr
T
f
4d
2
Gr
IN
G
C
2.5
3.8
4.8
5.5
4
S R
IN
) C
T
)
1/2
(
(pF)
) C
T
F
1/2
T
1/2
1/2
Gr
IN
)
C
AD813
T
1
150
125
f
105
95
2
(MHz)