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MAX3225EEAP+T 其他数据使用手册 - Maxim Integrated（美信）
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Maxim Integrated（美信）
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接口芯片
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SSOP-20
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MAX3225EEAP+T数据手册
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若手册格式错乱，请下载阅览PDF原文件
Figure 4. Noise pulse blanking.
The block diagram of the blanking circuit is Figure 5.
Figure 5. Noise-blanking block diagram.
From the basic concept of blanking in Figure 5, more elegance can be added. The input buffer may not
be needed if the source is low impedance. R1 and R2 set a DC value as shown in application note
4344, "Rail Splitter, from Abraham Lincoln to Virtual Ground," mentioned above. Alternatively, the input
signal could be AC coupled to this same voltage or the input signal could be averaged over the long
term to produce this voltage. The main signal path is from the input buffer through a RC delay, the mux,
buffer, and lowpass filter to the ADC. The MAX11203 ADC has four general-purpose input or output
(GPIO) ports controlled by the SPI interface. The GPIO is set so that the AIN1of the MAX313 multiplexor
is on and AIN2 is off. We highpass or differentiate the noise pulse. The dual or window comparator
output will be active while the noise pulse exceeds 0.3V in either the positive or negative direction. The
XOR gated inverts the logic to the mux, thereby turning off the main path and switching on the DC
voltage. The RC delay also delays the main path long enough for the comparator path to change state. If
the RC delay degrades the signal bandwidth too much, an LC delay line can be substituted.
The input buffer of Figure 5 could use a MAX4209 instrument amplifier which has incredibly low offset
drift despite its high gain. Application note 4179, "Autozero Noise Filtering Improves Instrumentation
Amplifier Output," explains why.
The filter just before the ADC in Figure 5 can control signal bandwidth to meet Nyquist anti-aliasing,
reduce noise, or soften the residual blanking glitch. The following application notes will provide advice
and ideas:
3077, "A Digitally Controllable Lowpass Filter Using a Digital Potentiometer"
928, "Filter Basics: Anti-Aliasing"
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