Monday, February 05, 2007

Wideband ADC Front-End Design: Amplifier Drive vs. Transformer Drive

The circuitry ahead of a high-performance ADC is critical to achieving desired system performance. The optimal design depends on many factors, including the application, system partition, and ADC architecture. Amplifiers consume power and add noise, whereas transformers consume no power and add negligible noise. On the other hand, amplifiers maintain dc levels, provide easily adjustable gain, and have flatter response.

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At 9:37 AM, Anonymous Anonymous said...

hi, it is very helpful article that i ever seen.
i want to know for example why in broadband applications (b)it suggest to use shunt or series inductor for switched-capacitor,what suggest for BiCMOS ADC for example AD9445 that has fixed impedance.
i read AN-835 and it explain switched-capacitor ADCs too,what is i must consider for BiCMOS ADCs for broadband applications?

At 9:55 AM, Anonymous Rob Reeder said...


Using buffered type BiCMOS ADCs are less critical when designing the front end vs. unbuffered (ie - switched-capacitor) types. The reason is buffered type ADCs have a fixed input impedance network that does not vary across frequency. Typical values are 1-2kohm differential in parallel with a 2-3pF capacitor. If you need additional help or advise you can contact me at


Rob Reeder


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