0
–1
–2 SINGLE OP AMP,
CONVENTIONAL
–3
DESIGN
–4
CASCADED
(TWO STAGES)
–5 LOW PHASE ERROR
AMPLIFIER
–6
–7
0.001
0.01
0.005
0.1
0.005
FREQUENCY RATIO – 1/ /
1.0
0.5
Figure 5. Phase Error Comparison
Figure 5 compares the phase error performance of the low
phase error amplifier with a conventional single op amp
amplifier and a cascaded two-stage amplifier. The low phase
error amplifier shows a much lower phase error, particularly for
frequencies where ր〉T<0.1. For example, phase error of
-0.1؇ occurs at 0.002 ր〉T for the single op amplifier, but
at 0.11 ր〉T for the low phase error amplifier.
For more detailed information on the low phase error amplifier,
see Application Note AN-107.
OP271
Dual 12-Bit Voltage Output DAC
The dual voltage output DAC shown in Figure 6 will settle to
12-bit accuracy from zero to full scale in 2 s typically. The
CMOS DAC-8222 utilizes a 12-bit, double-buffered input
structure allowing faster digital throughput and minimizing
digital feedback.
Fast Current Pump
Maximum output current of the fast current pump shown in
Figure 7 is ؎11 mA. Voltage compliance exceeds ؎10 V with
؎15 V supplies. The current pump has an output resistance
of over 3 M⍀ and maintains 12-bit linearity over its entire
output range.
R3
10k⍀
R1
10k⍀
VIN
R2
10k⍀
2
1/2
OP271FZ
3
R5
1
100⍀
+15V
R4
10k⍀
8
5
7
1/2
OP271FZ
6
4
IOUT
؎11mA
IOUT =
VIN
RS
= VIN =10mA/V
100⍀
–15V
Figure 7. Fast Current Pump
REV. A
+15V
10F
10V
REFERENCE
VOLTAGE
5V
21
VDD
DAC-8222EW
RFBA
3
4 VREFA
DAC A
IOUTA 2
10pF
2
3
12-BIT DATABUS PINS 6–17
AGND 1
0.1F
8
–
1/2
OP271EZ
+
4
0.1F
VOUTA
–15V
10F
22 VREFB
DAC B
IOUTB 24
6–
10pF
1/2
7
OP271EZ
18 DAC A/DAC B
RFBB
23
5+
DAC
CONTROL
19 LDAC
20 WR
DGND
VOUTB
Figure 6. Dual 12-Bit Voltage Output DAC
–9–