參數資料
型號: AD648CQ
廠商: ANALOG DEVICES INC
元件分類: 運動控制電子
英文描述: Dual Precision, Low Power BiFET Op Amp
中文描述: DUAL OP-AMP, 500 uV OFFSET-MAX, 1 MHz BAND WIDTH, CDIP8
封裝: CERDIP-8
文件頁數: 7/12頁
文件大?。?/td> 335K
代理商: AD648CQ
AD648
REV. C
–7–
SIGN BIT
BINARY NUMBER IN DAC REGISTER ANALOG OUTPUT
0
0
1
1
1111 1111 1111
0000 0000 0000
0000 0000 0000
1111 1111 1111
+V
IN
3
(4095/4096)
0 VOLTS
0 VOLTS
–V
IN
3
(4095/4096)
NOTE: SIGN BIT AT "0" CONNECTS THE NONINVERTING INPUT OF
A2 TO ANALOG COMMON
Figure 25. Sign Magnitude Code Table
Figure 23c shows a diode clamp protection scheme for an I-to-V
converter using low leakage diodes. Because the diodes are con-
nected to the op amp’s summing junction, which is a virtual
ground, their leakage contribution is minimal.
Figure 23c. I-to-V Converter with Diode Input Protection
Exceeding the negative common-mode range on either input
terminal causes a phase reversal at the output, forcing the ampli-
fier output to the corresponding high or low state. Exceeding
the negative common mode on both inputs simultaneously
forces the output high. Exceeding the positive common-mode
range on a single input doesn’t cause a phase reversal; but if
both inputs exceed the limit, the output will be forced high. In
all cases, normal amplifier operation is resumed when input
voltages are brought back within the common-mode range.
D/A CONVE RT E R BIPOLAR OUT PUT BUFFE R
T he circuit in Figure 24 provides 4 quadrant multiplication with
a resolution of 12 bits. T he AD648 is used to convert the AD7545
CMOS DAC’s output current to a voltage and provides the
necessary level shifting to achieve a bipolar voltage output. T he
circuit operates with a 12-bit plus sign input code. T he transfer
function is shown in Figure 25.
T he AD7592 is a fully protected dual CMOS SPDT switch with
data latches. R4 and R5 should match to within 0.01% to main-
tain the accuracy of the converter. A mismatch between R4 and
R5 introduces a gain error. Overall gain is trimmed by adjusting
R
IN
. T he AD648’s low input offset voltage, low drift over tem-
perature, and excellent dynamics make it an attractive low
power output buffer.
T he input offset voltage of the AD648 output amplifier results
in an output error voltage. T his error voltage equals the input
offset voltage of the op amp times the noise gain of the amplifier.
T hat is:
V
OS
Output
=
V
OS
Input
1
+
R
FB
R
O
R
FB
is the feedback resistor for the op amp, which is internal to
the DAC. R
O
is the DAC’s R-2R ladder output resistance. T he
value of R
O
is code dependent. T his has the effect of changing
the offset error voltage at the amplifier’s output. An output am-
plifier with a sub millivolt input offset voltage is needed to pre-
serve the linearity of the DAC’s transfer function.
Figure 24. 12-Bit Plus Sign Magnitude D/A Converter
相關PDF資料
PDF描述
AD648J Dual Precision, Low Power BiFET Op Amp
AD648K Dual Precision, Low Power BiFET Op Amp
AD648KN Dual Precision, Low Power BiFET Op Amp
AD648KR Dual Precision, Low Power BiFET Op Amp
AD648S Dual Precision, Low Power BiFET Op Amp
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