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P7001: Difference between revisions
added short description of the A/D converter card
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===Sample & Hold=== | ===Sample & Hold=== | ||
The functionality of the Sample & Hold card can be divided into 3 areas: Display switching, sampling and multiplexing. The display switching section determines which waveform (real time or stored) is sent to the CRT and is designed around two Tek-made analog multiplexer chips [[155-0022-00]]. A fast [[sampling diodes|four-diode sample and hold circuit]] is the heart of the sampling circuit. Regardless of sweep speed, the sample & Hold card takes a sample every 6.5us. At first the vertical axis is sampled, 95 nanoseconds later the horizontal axis and the blanking. In the last stage the sampled signals are time-multiplexed to provide one output to the A/D converter. The complete timing of the sample & hold circuits is controlled by the A/D Converter card. | The functionality of the Sample & Hold card can be divided into 3 areas: Display switching, sampling and multiplexing. The display switching section determines which waveform (real time or stored) is sent to the CRT and is designed around two Tek-made analog multiplexer chips [[155-0022-00]]. A fast [[sampling diodes|four-diode sample and hold circuit]] is the heart of the sampling circuit. Regardless of sweep speed, the sample & Hold card takes a sample every 6.5us. At first the vertical axis is sampled, 95 nanoseconds later the horizontal axis and the blanking. In the last stage the sampled signals are time-multiplexed to provide one output to the A/D converter. The complete timing of the sample & hold circuits is controlled by the A/D Converter card. | ||
===A/D Converter=== | |||
The A/D Converter uses a successive approximation technique to digitize the vertical and horizontal samples. The vertical resolution is 10 bits, the horizontal resolution 9 bits. It is worth mentioning that the vertical signal is digitized in a range of 10 divisions. As a result, even signal components that are slightly above or below the screen edge are captured. A two bit memory location code (A, B, C or D) is added to the converted horizontal data. The result is the direct memory address at which the vertical data is stored to. For sweeps slower or equal to 500 μs/Div all 512 waveform points are digitized in one sweep. For faster sweep speeds the samples will be taken out-of-order with respect to their equivalent time in the waveform. In this case subsequent sweeps are needed complete the digitized data. The computer has direct access to the register of the A/D converter and may at any time read the last vertical sample. This makes it possible to create arrays with more than 512 elements. | |||
===Hardware Signal Averager=== | ===Hardware Signal Averager=== | ||