参数资料
型号: AD7538AQ
厂商: Analog Devices Inc
文件页数: 4/16页
文件大小: 0K
描述: IC DAC 14BIT W/BUFF 24-CDIP
产品培训模块: Data Converter Fundamentals
DAC Architectures
标准包装: 15
设置时间: 1.5µs
位数: 14
数据接口: 并联
转换器数目: 1
电压电源: 单电源
功率耗散(最大): 1W
工作温度: -25°C ~ 85°C
安装类型: 通孔
封装/外壳: 24-CDIP(0.300",7.62mm)
供应商设备封装: 24-CDIP
包装: 管件
输出数目和类型: 1 电流,单极;1 电流,双极
采样率(每秒): 667k
AD7538
Rev. B | Page 12 of 16
PROGRAMMABLE GAIN AMPLIFIER
The circuit shown in Figure 9 provides a programmable gain
amplifier (PGA). In it the DAC behaves as a programmable
resistance and thus allows the circuit gain to be digitally
controlled.
AD7538
N
IOUT
VDD
VSS
VOUT
VIN
VREF
GND
DIGITAL
INPUT
A
RFB
NOTES
1. RESISTOR RFB IS ACTUALLY
INCLUDED ON THE DICE.
01
13
9-
00
9
Figure 9. Programmable Gain Amplifier (PGA)
The transfer function of Figure 9 is:
FB
EQ
IN
OUT
R
V
Gain
=
(1)
REQ is the equivalent transfer impedance of the DAC from the
VREF pin to the IOUT pin and can be expressed as
N
R
IN
n
EQ
2
=
(2)
where:
n
is the resolution of the DAC.
N
is the DAC input code in decimal.
RIN
is the constant input impedance of the DAC (RIN = RLAD).
Substituting this expression into Equation 1 and assuming
zero gain error for the DAC (RIN = RFB), the transfer function
simplifies to
N
V
n
IN
OUT
2
=
(3)
The ratio N/2n is commonly represented by the term, D, and, as
such, is the fractional representation of the digital input word.
D
N
V
n
IN
OUT
1
2
=
=
(4)
Equation 4 indicates that the gain of the circuit can be varied
from 16,384 down to unity (actually 16,384/16,383) in 16,383
steps. The all 0s code is never applied. This avoids an open-loop
condition thereby saturating the amplifier. With the all 0s code
excluded there remains (2n – 1) possible input codes allowing a
choice of (2n – 1) output levels. In decibels the dynamic range is
(
)
dB
84
1
2
log
20
log
20
10
=
=
n
IN
OUT
V
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