Datasheet OP271 (Analog Devices) - 9

OP271 Dual 12-Bit Voltage Output DAC 0
The dual voltage output DAC shown in Figure 6 will settle to
–1
12-bit accuracy from zero to full scale in 2 s typically. The CMOS DAC-8222 utilizes a 12-bit, double-buffered input
–2 SINGLE OP AMP,
structure allowing faster digital throughput and minimizing
CONVENTIONAL
digital feedback.
–3 DESIGN Fast Current Pump –4 CASCADED (TWO STAGES)
Maximum output current of the fast current pump shown in Figure 7 is 11 mA. Voltage compliance exceeds 10 V with
PHASE SHIFT – DEG –5 LOW PHASE ERROR AMPLIFIER
15 V supplies. The current pump has an output resistance
–6
of over 3 M and maintains 12-bit linearity over its entire output range.
–7 0.001 0.01 0.1 1.0 0.005 0.005 0.5 FREQUENCY RATIO – 1/ / R3 10k
Figure 5. Phase Error Comparison
R1
Figure 5 compares the phase error performance of the low
10k 2 R5
phase error amplifier with a conventional single op amp
1/2 100 1 I V OUT
amplifier and a cascaded two-stage amplifier. The low phase
IN R2 OP271FZ 11mA 10k 3
error amplifier shows a much lower phase error, particularly for
+15V
frequencies where T<0.1. For example, phase error of -0.1 occurs at 0.002 T for the single op amplifier, but
8 5 R4
at 0.11 T for the low phase error amplifier.
10k 1/2 7 OP271FZ
For more detailed information on the low phase error amplifier,
6
see Application Note AN-107.
4 V V I IN IN OUT = = =10mA/V RS 100 –15V
Figure 7. Fast Current Pump
+15V 10 F 5V 0.1 F 21 VDD RFBA 3 DAC-8222EW 8 10V 10pF REFERENCE V I VOLTAGE 4 REFA OUTA 2 2 DAC A – 1/2 OP271EZ V OBSOLETEOUTA 3 + AGND 1 4 –15V 12-BIT DATABUS PINS 6–17 0.1 F 10 F V I 22 REFB OUTB 24 6 DAC B – 1/2 7 10pF V OP271EZ OUTB RFBB 18 23 DAC A/DAC B 5 + DAC 19 LDAC CONTROL 20 WR DGND
Figure 6. Dual 12-Bit Voltage Output DAC REV. A –9– Document Outline FEATURES GENERAL DESCRIPTION PIN CONNECTIONS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE Typical Performance Characteristics APPLICATION INFORMATION Capacitive Load Driving and Power Supply Considerations Unity-Gain Buffer Applications Computer Simulations APPLICATIONS Low Phase Error Amplifier Dual 12-Bit Voltage Output DAC Fast Current Pump OUTLINE DIMENSIONS Revision History