Anatomy Of A Scope Front End

Oct. 5, 2010

LeCroy Corp. designed and developed two main chips for its WaveMaster 8 Zi-A: the track-and-hold chip and the monolithic 40-Gsample/s analog-to-digital converter (ADC), which is the world’s fastest single-component ADC. This track-and-hold chip is being used for the first time in the WaveMaster 8 Zi-A, whereas the ADC was previously deployed in the WavePro 7 Zi.

The company uses a fast track-and-hold switch system to route the signal into successive track-and-holds built into the chip. The track-and-hold bandwidth is 16 GHz. All functionality of the track-and-hold is on this one chip.

The clock controls when the track occurs and when the hold begins. It also controls when the switch moves to the next track-and-hold. Note that there are eight track-and-holds on this chip. By integrating the track-and-holds into one chip, high-frequency signals can be tracked precisely and then the digitizer measures the held value. This ensures signal fidelity in the highest bandwidth signals.

The ADC consists of eight 5-Gsample/s, 8-bit converters all on a single chip. Examining the chip reveals eight rectangular sections, and each one is a 5-Gsample/s ADC. Built into the chip is the precise ability to time the phasing of the ADCs to achieve 40 Gsamples/s and to match the offsets between individual ADCs.

Also on this chip is the memory de-multiplexer. The data is pushed out so fast from the ADC that it needs to be fanned out to several memory devices, all of which are built into the chip. And, LeCroy uses its own custom memory chip on four memory plug-in cards to achieve 256 Mpoints/channel of memory.

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