OP-44_15 Datasheet, PDF (8/9 Pages) Analog Devices – HIGH SPEED PRECISION OPERATIONAL AMPLIFIER

!PMI) OP-44 HIGH-SPEED, PRECISION OPERATIONAL AMPLIFIER
Digital offset correction is possible using the nulling pins. The
circuit of Figure 5 will correct for greater than :t4mV of offset,
allowing correction of some system errors in addition to the
OP-44's offset voltage. One of the four voltage-output DACs on
the PM-7226 is used to apply a voltage between OVand 10Vto
the 200kfl resistor, while the 255kfl resistor is tied to the +10V
reference. One LSB of the 8-bit PM-7226 is equivalent to
approximately 35p.V of offset change around the zero offset
point.
FIGURE 6: High-Speed, Low-Offset, Low-Drift Amplifier
RI
R2
2kO
V'N
VOUT
FIGURE 5: Digital Offset Correction
.
~ I"F
R1
R2
+15V
OB_{--- S} ^{- - - REF-O1.6}
255kO
2ookO
VAEF
1/4
PM-7226
DIGITAL
INPUT
OL _{A common problem with many high-speed amplifiers is a}
E _{requirement for more DC precision than the amplifier's capa-}
T ^{bility. While the OP-44 already offers an order of magnitude or}
E ^{more improvements in precision over previous high-speed}
2kO
18kO
FIGURE 7: Combination Amplifier Transient Response
,II,
.
r
l
'i""
I
m
FIGURE8: Combination AmplifierVas vs Temperature
amplifiers, some users may find a need for even greater
precision.
Figure 6 shows a combination amplifier melding the precision
DC characteristics of an OP-97 with the high speed of the
OP-44. The OP-97 reacts for low-frequency and DC signals,
while the OP-44 is dominant at higher frequencies. Over-
compensation of the OP-97 ensures that it operates only at low
frequencies. Resistor matching is important to optimize this
circuit's transient response. The overall supply current of this
combination amplifier is only slightly higher than that of the
OP-44 alone. This is due to the minimal consumption of the
OP-97, only 600p.A.Transient response of this circuit is shown in
Figure 7. Its initial offset voltage is 20p.V,while TCVos is less than
O.6p.V!°C.
100
:;
~
80
w
"_~ 60
I
Vs=:t15V
Vcu=OV
~_.... 40
w_'"
-- ^{I0t 20}
Q
wa:
w_.^a:_.
---^/
::! -20
~::>
~ -40
./
./
-60
-so -25
0255075
V
./
100 125
TEMPERATURE(OC)
.
8
--~
~-
.
10/87, Rev. 81