- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄3421 > AD640BD (Analog Devices Inc)IC AMP LOG 2.3MA 20CDIP PDF資料下載
參數(shù)資料
| 型號： | AD640BD |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 16/16頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC AMP LOG 2.3MA 20CDIP |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 放大器類型： | 對數(shù) |
| 電路數(shù)： | 1 |
| -3db帶寬： | 350MHz |
| 電流 - 輸入偏壓： | 7µA |
| 電壓 - 輸入偏移： | 50µV |
| 電流 - 電源： | 35mA |
| 電流 - 輸出 / 通道： | 2.3mA |
| 電壓 - 電源，單路/雙路(±)： | ±4.5 V ~ 7.5 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 通孔 |
| 封裝/外殼： | 20-CDIP（0.300"，7.62mm） |
| 供應(yīng)商設(shè)備封裝： | 20-CDIP |
| 包裝： | 管件 |
AD640
REV. C
–9–
(see Figure 20). For the AD640, VX is calibrated to exactly
1 mV. The slope of the line is directly proportional to VY. Base
10 logarithms are used in this context to simplify the relation-
ship to decibel values. For VIN = 10 VX, the logarithm has a
value of 1, so the output voltage is VY. At VIN = 100 VX, the
output is 2 VY, and so on. VY can therefore be viewed either as
the Slope Voltage or as the Volts per Decade Factor.
0
VY
2VY
VIN = VX
VIN = 10VX
VIN = 100VX
SLOPE = VY
ACTUAL
IDEAL
INPUT ON
LOG SCALE
ACTUAL
IDEAL
VYLOG (VIN/VX)
Figure 20. Basic DC Transfer Function of the AD640
The AD640 conforms to Equation (1) except that its two out-
puts are in the form of currents, rather than voltages:
IOUT = IY LOG (VIN/VX)
Equation (2)
IY the Slope Current, is 1 mA. The current output can readily be
converted to a voltage with a slope of 1 V/decade, for example,
using one of the 1 k
resistors provided for this purpose, in
conjunction with an op amp, as shown in Figure 21.
11
15
14
13
12
6
7
8
9
10
SIG
+OUT
LOG
COM
LOG
OUT
+VS
–VS
ITC
BL2
SIG
–OUT
AD640
C1
330pF
AD844
R1
48.7
R2
1mA PER
DECADE
OUTPUT VOLTAGE
1V PER DECADE
FOR R2 = 1k
100mV PER dB
for R2 = 2k
Figure 21. Using an External Op Amp to Convert the
AD640 Output Current to a Buffered Voltage Output
Intercept Stabilization
Internally, the intercept voltage is a fraction of the thermal volt-
age kT/q, that is, VX = VXOT/TO, where VXO is the value of VX
at a reference temperature TO. So the uncorrected transfer
function has the form
IOUT = IY LOG (VIN TO/VXOT)
Equation (3)
Now, if the amplitude of the signal input VIN could somehow be
rendered PTAT, the intercept would be stable with tempera-
ture, since the temperature dependence in both the numerator
and denominator of the logarithmic argument would cancel.
This is what is actually achieved by interposing the on-chip
attenuator, which has the necessary temperature dependence to
cause the input to the first stage to vary in proportion to abso-
lute temperature. The end limits of the dynamic range are now
totally independent of temperature. Consequently, this is the
preferred method of intercept stabilization for applications
where the input signal is sufficiently large.
When the attenuator is not used, the PTAT variation in VX
will result in the intercept being temperature dependent. Near
300K (27
°C) it will vary by 20 LOG (301/300) dB/°C, about
0.03 dB/
°C. Unless corrected, the whole output function would
drift up or down by this amount with changes in temperature. In
the AD640 a temperature compensating current IYLOG(T/TO)
is added to the output. This effectively maintains a constant
intercept VXO. This correction is active in the default state (Pin
8 open circuited). When using the attenuator, Pin 8 should be
grounded, which disables the compensation current. The drift
term needs to be compensated only once; when the outputs of
two AD540s are summed, Pin 8 should be grounded on at least
one of the two devices (both if the attenuator is used).
Conversion Range
Practical logarithmic converters have an upper and lower limit
on the input, beyond which errors increase rapidly. The upper
limit occurs when the first stage in the chain is driven into limit-
ing. Above this, no further increase in the output can occur and
the transfer function flattens off. The lower limit arises because
a finite number of stages provide finite gain, and therefore at
low signal levels the system becomes a simple linear amplifier.
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 AD640s 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 AD640 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
baseband 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
AD640s 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.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| 66506-052 | QUICKIE HEADER2X17 D |
| 68782-236H | BERGSTIK II SR RIGHT ANGLE |
| 67997-420H | BERGSTIK II .100" DR STRAIGHT |
| 77311-119-16LF | BERGSTIK |
| 78576-472 | BERGSTIK II DR R/A WIDE BODY |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD640BE | 功能描述:IC AMP LOG 2.3MA 20CLCC RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 其它有關(guān)文件:TS1854A View All Specifications 標(biāo)準(zhǔn)包裝:50 系列:- 放大器類型:通用 電路數(shù):4 輸出類型:滿擺幅 轉(zhuǎn)換速率:0.25 V/µs 增益帶寬積:630kHz -3db帶寬:- 電流 - 輸入偏壓:16nA 電壓 - 輸入偏移:1000µV 電流 - 電源:162µA 電流 - 輸出 / 通道:48mA 電壓 - 電源，單路/雙路(±):1.8 V ~ 6 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:14-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:14-SO 包裝:管件 |
| AD640BP | 功能描述:IC AMP LOG 2.3MA 20PLCC RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 其它有關(guān)文件:TS1854A View All Specifications 標(biāo)準(zhǔn)包裝:50 系列:- 放大器類型:通用 電路數(shù):4 輸出類型:滿擺幅 轉(zhuǎn)換速率:0.25 V/µs 增益帶寬積:630kHz -3db帶寬:- 電流 - 輸入偏壓:16nA 電壓 - 輸入偏移:1000µV 電流 - 電源:162µA 電流 - 輸出 / 通道:48mA 電壓 - 電源，單路/雙路(±):1.8 V ~ 6 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:14-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:14-SO 包裝:管件 |
| AD640BPZ | 功能描述:IC AMP LOG 2.3MA 20PLCC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 放大器類型:通用 電路數(shù):4 輸出類型:滿擺幅 轉(zhuǎn)換速率:0.028 V/µs 增益帶寬積:105kHz -3db帶寬:- 電流 - 輸入偏壓:3nA 電壓 - 輸入偏移:100µV 電流 - 電源:3.3µA 電流 - 輸出 / 通道:12mA 電壓 - 電源，單路/雙路(±):2.7 V ~ 12 V，±1.35 V ~ 6 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:14-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:14-TSSOP 包裝:剪切帶 (CT) 其它名稱:OP481GRUZ-REELCT |
| AD640EB | 制造商:AD 制造商全稱:Analog Devices 功能描述:DC-Coupled Demodulating 120 MHz Logarithmic Amplifier |
| AD640-EB | 制造商:Analog Devices 功能描述: |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。