AD668 AD [Analog Devices], AD668 Datasheet - Page 10

• Manufacturer Part Number: AD668
• Description: 12-Bit Ultrahigh Speed Multiplying D/A Converter
• Manufacturer: AD [Analog Devices]

AD668
Nominal
Analog
Input
1 V
1.25 V
5 V
mode (Pin 22 grounded, input into Pin 21). Fine adjustment of
the gain is provided by both the AD586 external trim resistor
and the 100
The resistive divider at the reference input will draw approxi-
mately 1 mA from the AD586, leaving plenty of driving current
for other loads in the system.
AC HOOKUP: 1.25 V AC FULL SCALE, 2.5 V DC FULL
SCALE
The circuit shown in Figure 12 allows separate setting of dc ref-
erence bias point on a 2.5 V scale and capacitively coupled ac
signal on a 1.25 V scale. The basic reference input is configured
in the 1.25 V mode (Pin 21 grounded, Pin 22 used as the refer-
ence input.) The 2.5 V dc range is achieved by using an external
Figure 11. AD586 Driving the AD668
0 V to 1 V
Unipolar
Unbuffered V
A
Unipolar
Unbuffered V
A
Pin 21 Grounded
Unipolar
Unbuffered V
A
Pin 22 Grounded
(See Figure 7)
IN
IN
IN
potentiometer in series with the reference input.
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
–500 mV to +500 mV
Bipolar
Unbuffered V
A
Bipolar
Unbuffered V
A
Pin 21 Grounded
(See Figure 8)
Bipolar
Unbuffered V
A
Pin 22 Grounded
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
Table II. AD668 Topology Variations
OUT
OUT
OUT
OUTPUT LEVELS
–10–
0 V to –10 V
Unipolar
Buffered V
A
External Amplifier
(See Figure 10)
Unipolar
Buffered V
A
Pin 21 Grounded
External Amplifier
Unipolar
Buffered V
A
Pin 22 Grounded
External Amplifier
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
5k series resistor in the dc path. Note that because of the rela-
tively wide tolerance ( 20%) in the absolute value of the
AD668’s internal input divider resistors, substantial gain range
adjustment should be provided in the external series resistance.
DAC DRIVE: THE AD568 DRIVING THE AD668
The circuit shown in Figure 13 produces an analog output pro-
portional to the product of two digital inputs. The AD568 has
an on-board fixed reference and generates a full-scale output
voltage of 1.024 V (just as the AD668 does in its unbuffered
voltage output mode). This output voltage can be used to di-
rectly drive the AD668 in the 1 V reference input mode. Note
that in this case, the lower 410 codes of the AD568 are out-of-
bounds; they produce an undervoltage condition at the AD668
OUT
OUT
OUT
+5 V to –5 V
Bipolar
Buffered V
A
External Amplifier
Bipolar
Buffered V
A
Pin 21 Grounded
External Amplifier
Bipolar
Buffered V
A
Pin 22 Grounded
External Amplifier
Figure 12. AC Hookup
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
–1 V to +1 V
Bipolar
Unbuffered V
A
R
To I
Bipolar
Unbuffered V
A
Pin 21 Grounded
R
To I
Bipolar
Unbuffered V
A
Pin 22 Grounded
R
To I
(See Figure 9)
IN
L
IN
L
IN
L
(Pin 19) Tied
(Pin 19) Tied
(Pin 19) Tied
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
(Pin 20)
(Pin 20)
(Pin 20)
REV. A
OUT
OUT
OUT