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ICL7650ITV-1 参数 Datasheet PDF下载

ICL7650ITV-1图片预览
型号: ICL7650ITV-1
PDF下载: 下载PDF文件 查看货源
内容描述: 零漂移运算放大器 [Zero-Drift Operational Amplifier]
分类和应用: 运算放大器斩波器
文件页数/大小: 24 页 / 846 K
品牌: Linear [ Linear ]
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LTC1052/LTC7652  
U
THEORY OF OPERATIO  
power supply are also nulled. For nulling to take place, the  
offset voltage, common mode voltage and power supply  
must not change at a frequency which is high compared to  
the frequency response of the nulling loop.  
For frequencies above this pole, I2 is:  
1
SC2  
I2 = VIN gm6  
• SC1  
and  
C1  
C2  
I1 – I2 = VIN gm1 – VIN gm6  
AC OPERATION AND ALIASING ERRORS  
The LTC1052 is very carefully designed so that gm1 = gm6  
and C1 = C2. Substituting these values in the above equa-  
tion shows I1 – I2 = 0.  
So far, the DC performance of the LTC1052 has been  
explained. As the input signal frequency increases, the  
problem of aliasing must be addressed. Aliasing is the  
spurious formation of low and high frequency signals  
caused by the mixing of the input signal with the sampling  
frequency, fS. The frequency of the error signals, fE, is:  
The gm6 input stage, with Cl and C2, not only filters the  
input to the sampling loop, but also acts as a high  
frequency path to give the LTC1052 good high frequency  
response. The unity-gain cross frequencies for both the  
DC path and high frequency path are identical  
fE = fS ±fI  
where fI = input signal frequency.  
1
2π  
1
2π  
[f3dB =  
(gm1/C1) =  
(gm6/C2)]  
Normally it is the difference frequency (fS – fI ) which is of  
concern because the high frequency (fS + fI) can be easily  
filtered. As the input frequency approaches the sampling  
frequency, the difference frequency approaches zero and  
willcauseDCerrors—theexactproblemthatthezero-drift  
amplifier is meant to eliminate.  
thereby making the frequency response smooth and con-  
tinuous while eliminating sampling noise in the output as  
the loop transitions from the high gain DC loop to the high  
frequency loop.  
The typical curves show just how well the amplifier works.  
The output spectrum shows that the difference frequency  
(fI–fS = 100Hz) is down by 80dB and the frequency  
response curve shows no abnormalities or perturbations.  
Also note the well-behaved small and large-signal step  
responses and the absence of the sampling frequency in  
the output spectrum. If the dynamics of the amplifier  
(i.e., slew rate and overshoot), depend on the sampling  
clock, the sampling frequency will appear in the output  
spectrum.  
Thesolutionissimple;filtertheinputsothesamplingloop  
never sees any frequency near the sampling frequency.  
At a frequency well below the sampling frequency, the  
LTC1052 forces I1 to equal I2 (see Figure 1b). This makes  
δ l zero, thus the gain of the sampling loop zero at this and  
higher frequencies (i.e., a low pass filter). The corner  
frequency of this low pass filter is set by the output stage  
pole (1/RL4 gm5 RL5 C2).  
C1  
S3  
V
REF  
C2  
+ IN  
– IN  
S2  
S1  
+
+
g
g
m2  
g
+
g
+
V
m1  
m5  
m4  
OUT  
R
R
L2  
C
C
L1  
EXT B  
R
R
L4  
L5  
EXT A  
V
NULL  
g
m3  
V –  
g
m6  
LTC1052/7652 • TPC13  
+
Figure 1a. LTC1052 Block Diagram  
Auto Zero Cycle  
1052fa  
7
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