Datasheet

Data Sheet AD5450/AD5451/AD5452/AD5453
Rev. G | Page 17 of 28
Bipolar Mode
In some applications, it may be necessary to generate a full
4-quadrant multiplying operation or a bipolar output swing.
This can be easily accomplished by using another external
amplifier and some external resistors, as shown in Figure 45. In
this circuit, the second amplifier, A2, provides a gain of 2.
Biasing the external amplifier with an offset from the reference
voltage results in full 4-quadrant multiplying operation. The
transfer function of this circuit shows that both negative and
positive output voltages are created as the input data (D) is
incremented from Code 0 (V
OUT
= − V
REF
) to midscale
(V
OUT
− 0 V ) to full scale (V
OUT
= +V
REF
).
REF
n
REF
OUT
V
D
VV −






×=
−1
2
where:
D is the fractional representation of the digital word loaded to
the DAC.
D = 0 to 255 (8-bit AD5450).
= 0 to 1023 (10-bit AD5451).
= 0 to 4095 (12-bit AD5452).
n is the resolution of the DAC.
When V
IN
is an ac signal, the circuit performs 4-quadrant
multiplication. Table 6 shows the relationship between the
digital code and the expected output voltage for a bipolar
operation using the 8-bit AD5450.
Table 6. Bipolar Code Table for the AD5450
Digital Input Analog Output (V)
1111 1111 +V
REF
(127/128)
1000 0000 0
0000 0001 −V
REF
(127/128)
0000 0000 −V
REF
(128/128)
04587-010
NOTES
1. R1 AND R2 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
ADJUST R1 FOR V
OUT
= 0V WITH CODE 10000000 LOADED TO DAC.
2. MATCHING AND TRACKING IS ESSENTIAL FOR RESISTOR PAIRS
R3 AND R4.
3. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
IF A1/A2 IS A HIGH SPEED AMPLIFIER.
R
FB
I
OUT
1
GND
SCLK SDIN
V
REF
±10V
V
REF
R1
SYNC
AD5450/
AD5451/
AD5452/
AD5453
V
DD
V
DD
AGND
C1
A1
A2
R2
V
OUT
= –V
REF
TO +V
REF
µCONTROLLER
R3
20kΩ
R4
10kΩ
R5
20kΩ
Figure 45. Bipolar Mode Operation (4-Quadrant Multiplication)