参数资料
| 型号： | AD641AP |
| 厂商： | Analog Devices Inc |
| 文件页数： | 16/16页 |
| 文件大小： | 0K |
| 描述： | IC AMP LOG LP 2.3MA 20PLCC |
| 标准包装： | 1 |
| 放大器类型： | 对数 |
| 电路数： | 1 |
| -3db带宽： | 250MHz |
| 电流 - 输入偏压： | 7µA |
| 电压 - 输入偏移： | 50µV |
| 电流 - 电源： | 35mA |
| 电流 - 输出 / 通道： | 2.3mA |
| 电压 - 电源，单路/双路(±)： | ±4.5 V ~ 7.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-LCC（J 形引线） |
| 供应商设备封装： | 20-PLCC（9x9） |
| 包装： | 管件 |
REV. C
AD641
–9–
Note that this lower limit is not determined by the intercept
voltage, VX; it can occur either above or below VX, depending
on the design. When using two AD641s in cascade, input offset
voltage and wideband noise are the major limitations to low
level accuracy. Offset can be eliminated in various ways. Noise
can only be reduced by lowering the system bandwidth, using a
filter between the two devices.
EFFECT OF WAVEFORM ON INTERCEPT
The absolute value response of the AD641 allows inputs of
either polarity to be accepted. Thus, the logarithmic output in
response to an amplitude-symmetric square wave is a steady
value. For a sinusoidal input the fluctuating output current will
usually be low-pass filtered to extract the baseband signal. The
unfiltered output is at twice the carrier frequency, simplifying the
design of this filter when the video bandwidth must be maxi-
mized. The averaged output depends on waveform in a roughly
analogous way to waveform dependence of rms value. The effect
is to change the apparent intercept voltage. The intercept volt-
age appears to be doubled for a sinusoidal input, that is, the
averaged output in response to a sine wave of amplitude (not rms
value) of 20 mV would be the same as for a dc or square wave
input of 10 mV. Other waveforms will result in different inter-
cept factors. An amplitude-symmetric-rectangular waveform has
the same intercept as a dc input, while the average of a base-
band unipolar pulse can be determined by multiplying the
response to a dc input of the same amplitude by the duty cycle.
It is important to understand that in responding to pulsed RF
signals it is the waveform of the carrier (usually sinusoidal) not
the modulation envelope, that determines the effective intercept
voltage. Table I shows the effective intercept and resulting deci-
bel offset for commonly occurring waveforms. The input wave-
form does not affect the slope of the transfer function. Figure 22
shows the absolute deviation from the ideal response of cascaded
AD641s for three common waveforms at input levels from
–80 dBV to –10 dBV. The measured sine wave and triwave
responses are 6 dB and 8.7 dB, respectively, below the square
wave response—in agreement with theory.
Table I.
Input
Peak
Intercept
Error (Relative
Waveform
or rms
Factor
to a DC Input)
Square Wave
Either
1
0.00 dB
Sine Wave
Peak
2
–6.02 dB
Sine Wave
rms
1.414 (
√2)
–3.01 dB
Triwave
Peak
2.718 (e)
–8.68 dB
Triwave
rms
1.569 (e/
√3)
–3.91 dB
Gaussian Noise
rms
1.887
–5.52 dB
Logarithmic Conformance and Waveform
The waveform also affects the ripple, or periodic deviation from
an ideal logarithmic response. The ripple is greatest for dc or
square wave inputs because every value of the input voltage
maps to a single location on the transfer function and thus traces
out the full nonlinearities in the logarithmic response.
2
0
–2
–4
–6
–8
–10
–70
–60
–50
–40
–30
–20
–10
–80
INPUT AMPLITUDE IN dB ABOVE 1V, AT 10kHz
SQUARE
WAVE INPUT
SINE WAVE
INPUT
TRIWAVE
INPUT
DEVIATION
FROM
EXACT
LOGARITHMIC
TRANSFER
FUNCTION
–
dB
Figure 22. Deviation from Exact Logarithmic Transfer
Function for Two Cascaded AD641s, Showing Effect of
Waveform on Calibration and Linearity
By contrast, a general time varying signal has a continuum of
values within each cycle of its waveform. The averaged output is
thereby “smoothed” because the periodic deviations away from
the ideal response, as the waveform “sweeps over” the transfer
function, tend to cancel. This smoothing effect is greatest for a
triwave input, as demonstrated in Figure 22.
The accuracy at low signal inputs is also waveform dependent.
The detectors are not perfect absolute value circuits, having a
sharp “corner” near zero; in fact they become parabolic at low
levels and behave as if there were a dead zone. Consequently,
the output tends to be higher than ideal. When there are enough
stages in the system, as when two AD641s are connected in
cascade, most detectors will be adequately loaded due to the
high overall gain, but a single AD641 does not have sufficient
gain to maintain high accuracy for low level sine wave or triwave
inputs. Figure 23 shows the absolute deviation from calibration
for the same three waveforms for a single AD641. For inputs
between –10 dBV and –40 dBV the vertical displacement of the
traces for the various waveforms remains in agreement with the
predicted dependence, but significant calibration errors arise at
low signal levels.
4
2
0
–2
–4
–6
–8
–10
–70
INPUT AMPLITUDE IN dB ABOVE 1V, AT 10kHz
–60
–50
–40
–30
–20
–10
–12
DEVIATION
FROM
EXACT
LOGARITHMIC
TRANSFER
FUNCTION
–
dB
SQUARE
WAVE INPUT
SINE WAVE
INPUT
TRIWAVE
INPUT
Figure 23. Deviation from Exact Logarithmic Transfer
Function for a Single AD641, Compare Low Level
Response with That of Figure 22
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD641AP-REEL7 | 功能描述:IC AMP LOG LP 2.3MA 20PLCC RoHS:否 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:50 系列:- 放大器类型:J-FET 电路数:2 输出类型:- 转换速率:3.5 V/µs 增益带宽积:1MHz -3db带宽:- 电流 - 输入偏压:30pA 电压 - 输入偏移:2000µV 电流 - 电源:200µA 电流 - 输出 / 通道:- 电压 - 电源，单路/双路(±):7 V ~ 36 V，±3.5 V ~ 18 V 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:8-DIP（0.300"，7.62mm） 供应商设备封装:8-PDIP 包装:管件 |
| AD641APZ | 功能描述:IC AMP LOG LP 2.3MA 20PLCC RoHS:是 类别:集成电路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 标准包装:50 系列:- 放大器类型:J-FET 电路数:2 输出类型:- 转换速率:3.5 V/µs 增益带宽积:1MHz -3db带宽:- 电流 - 输入偏压:30pA 电压 - 输入偏移:2000µV 电流 - 电源:200µA 电流 - 输出 / 通道:- 电压 - 电源，单路/双路(±):7 V ~ 36 V，±3.5 V ~ 18 V 工作温度:0°C ~ 70°C 安装类型:通孔 封装/外壳:8-DIP（0.300"，7.62mm） 供应商设备封装:8-PDIP 包装:管件 |
| AD641-EB | 制造商:Analog Devices 功能描述:AD641 EVALUATION BOARD - Bulk |
| AD641N | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Amplifier. Other |
| AD641P | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Amplifier. Other |
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