AD844_07 AD [Analog Devices], AD844_07 Datasheet - Page 11

• Manufacturer Part Number: AD844_07
• Description: 60 MHz, 2000 V/us Monolithic Op Amp
• Manufacturer: AD [Analog Devices]

Noise
Noise sources can be modeled in a manner similar to the dc bias
currents, but the noise sources are I
induced noise at the output, V
Overall noise can be reduced by keeping all resistor values to a
minimum. With typical numbers, R1 = R2 = 1 kΩ, R
Vn = 2 nV/√Hz, Inp = 10 pA/√Hz, Inn = 12 pA/√Hz, V
calculates to 12 nV/√Hz. The current noise is dominant in
this case, as it will be in most low gain applications.
Video Cable Driver Using
The AD844 can be used to drive low impedance cables. Using
± 5 V supplies, a 100 Ω load can be driven to ± 2.5 V with low
distortion. Figure 11a shows an illustrative application which
provides a noninverting gain of 2, allowing the cable to be
reverse-terminated while delivering an overall gain of +1 to the
load. The –3 dB bandwidth of this circuit is typically 30 MHz.
Figure 11b shows a differential gain and phase test setup. In
video applications, differential-phase and differential-gain
characteristics are often important. Figure 11c shows the varia-
tion in phase as the load voltage varies. Figure 11d shows the
gain variation.
GENERATOR
STAIRCASE
ANALYZER
NETWORK
HP3314A
HP8753A
V
ON
V
SYNC OUT
EXT
TRIG
IN
50
= ((Inp R
RF OUT
OUT
R
3
2
(TERMINATOR)
P
–5V
+5V
)
2
4
OUT
7
+ Vn
IN
6
2.2 F
5 Volt Supplies
2.2 F
ON
50
HP11850C
SPLITTER
2
, is:
) 1 +



NN
300
OUT
300
50
, I
R2
R1
NP
Z
OUT
O
, V
= 50



2
N
+ (Inn R1)
V
V
, and the amplifier
IN
470
IN
R
50
CIRCUIT
UNDER
L
TEST
V
OUT
2
P
V
= 0,
OUT
ON
High Speed DAC Buffer
The AD844 performs very well in applications requiring
current-to-voltage conversion. Figure 12 shows connections for
use with the AD568 current output DAC. In this application the
bipolar offset is used so that the full-scale current is ± 5.12 mA,
which generates an output of ± 5.12 V usingdecoupling and
grounding techniques to achieve the full 12-bit accuracy and
realize the fast settling capabilities of the system. The unmarked
capacitors in this figure are 0.1 µF ceramic (for the 1 kΩ appli-
cation resistor on the AD568. Figure 13 shows the full-scale
transient response. Care is needed in power supply example,
AVX Type SR305C104KAA), and the ferrite inductors should
be about 2.5 µH (for example, Fair-Rite Type 2743002122).
The AD568 data sheet should be consulted for more complete
details about its use.
–0.06
–0.02
–0.04
0.06
0.04
0.02
–0.1
–0.2
–0.3
0.3
0.2
0.1
0
0
0
0
IRE = 7.14mV
IRE = 7.14mV
18
18
Applications–
36
36
V
V
OUT
OUT
– IRE
– IRE
54
54
72
72
AD844
90
90