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参数资料
| 型号： | AD7703CNZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 15/16页 |
| 文件大小： | 0K |
| 描述： | IC ADC 20BIT LC2MOS MONO 20-DIP |
| 标准包装： | 1 |
| 位数： | 20 |
| 采样率（每秒）： | 4k |
| 数据接口： | 串行 |
| 转换器数目： | 1 |
| 功率耗散（最大）： | 37mW |
| 电压电源： | 模拟和数字，双 ± |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 20-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 20-PDIP |
| 包装： | 管件 |
| 输入数目和类型： | 1 个单端，单极；1 个单端，双极 |
REV. E
–8–
AD7703
DIGITAL FILTERING
The AD7703’s digital filter behaves like an analog filter, with a
few minor differences.
First, since digital filtering occurs after the analog-to-digital
conversion, it can remove noise injected during the conversion
process. Analog filtering cannot do this.
On the other hand, analog filtering can remove noise superim-
posed on the analog signal before it reaches the ADC. Digital
filtering cannot do this and noise peaks riding on signals near
full scale have the potential to saturate the analog modulator and
digital filter, even though the average value of the signal is within
limits. To alleviate this problem, the AD7703 has overrange
headroom built into the
-
modulator and digital filter that
allows overrange excursions of 100 mV. If noise signals are larger
than this, consideration should be given to analog input filtering,
or to reducing the gain in the input channel so that a full-scale
input (2.5 V) gives only a half-scale input to the AD7703 (1.25 V).
This will provide an overrange capability greater than 100% at
the expense of reducing the dynamic range by one bit (50%).
FILTER CHARACTERISTICS
The cutoff frequency of the digital filter is fCLK/409600. At the
maximum clock frequency of 4.096 MHz, the cutoff frequency
of the filter is 10 Hz and the data update rate is 4 kHz.
Figure 9 shows the filter frequency response. This is a six-pole
Gaussian response that provides 55 dB of 60 Hz rejection for a
10 Hz cutoff frequency. If the clock frequency is halved to give a
5 Hz cutoff, 60 Hz rejection is better than 90 dB.
1
10
100
FREQUENCY – Hz
20
0
–20
–40
–60
–80
–100
–120
–140
–160
GAIN
–
dB
f
CLK = 1MHz
f
CLK = 2MHz
f
CLK = 4MHz
Figure 9. Frequency Response of AD7703 Filter
Since the AD7703 contains this low-pass filtering, there is a
settling time associated with step function inputs, and data will
be invalid after a step change until the settling time has elapsed.
The AD7703 is, therefore, unsuitable for high speed multiplex-
ing, where channels are switched and converted sequentially at
high rates, as switching between channels can cause a step change
in the input. However, slow multiplexing of the AD7703 is
possible, provided that the settling time is allowed to elapse
before data for the new channel is accessed.
The output settling of the AD7703 in response to a step input
change is shown in Figure 10. The Gaussian response has fast
settling with no overshoot, and the worst-case settling time to
±0.0007% is 125 ms with a 4.096 MHz master clock frequency.
PERCENT
OF
FINAL
V
ALUE
100
80
60
40
20
0
040
80
120
160
TIME – ms
Figure 10. AD7703 Step Response
USING THE AD7703
SYSTEM DESIGN CONSIDERATIONS
The AD7703 operates differently from successive approximation
ADCs or integrating ADCs. Since it samples the signal continu-
ously, like a tracking ADC, there is no need for a start convert
command. The 20-bit output register is updated at a 4 kHz rate,
and the output can be read at any time, either synchronously or
asynchronously.
CLOCKING
The AD7703 requires a master clock input, which may be an exter-
nal TTL/CMOS compatible clock signal applied to the CLKIN
pin (CLKOUT not used). Alternatively, a crystal of the correct
frequency can be connected between CLKIN and CLKOUT,
when the clock circuit will function as a crystal controlled oscillator.
Figure 11 shows a simple model of the on-chip gate oscillator
and Table II gives some typical capacitor values to be used with
various resonators.
AD7703
C2*
C1*
R1
5M
X1
3
10pF
gm = 1500 MHO
*SEE TABLE II
2
Figure 11. On-Chip Gate Oscillator
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD7703CQ | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| AD7703CR | 功能描述:IC ADC 20BIT LC2MOS MONO 20-SOIC RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:- 位数:14 采样率（每秒）:83k 数据接口:串行，并联 转换器数目:1 功率耗散（最大）:95mW 电压电源:双 ± 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:28-DIP（0.600"，15.24mm） 供应商设备封装:28-PDIP 包装:管件 输入数目和类型:1 个单端，双极 |
| AD7703CR-REEL | 功能描述:IC ADC 20BIT LC2MOS MONO 20-SOIC RoHS:否 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:- 位数:14 采样率（每秒）:83k 数据接口:串行，并联 转换器数目:1 功率耗散（最大）:95mW 电压电源:双 ± 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:28-DIP（0.600"，15.24mm） 供应商设备封装:28-PDIP 包装:管件 输入数目和类型:1 个单端，双极 |
| AD7703CRZ | 功能描述:IC ADC 20BIT LC2MOS MONO 20SOIC RoHS:是 类别:集成电路 (IC) >> 数据采集 - 模数转换器 系列:- 标准包装:1 系列:- 位数:14 采样率（每秒）:83k 数据接口:串行，并联 转换器数目:1 功率耗散（最大）:95mW 电压电源:双 ± 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:28-DIP（0.600"，15.24mm） 供应商设备封装:28-PDIP 包装:管件 输入数目和类型:1 个单端，双极 |
| AD7703SQ | 制造商:AD 制造商全称:Analog Devices 功能描述:LC2MOS 20-Bit A/D Converter |
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