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Analog to Digital Converter

An analog-to-digital converter (ADC) generates a digital word proportional to the amplitude of an input pulse. In nuclear applications, ADCs are used to digitize the output signals from spectroscopy amplifiers. Since these amplifiers generate output pulses whose amplitudes are directly proportional to the energies of the incident radiation, the ADC can be used with an amplifier and a multichannel analyzer (MCA) to generate energy distributions (spectra) of radioactive samples.

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Model 8701 Analog-to-Digital Converter

Model 8701 Analog-to-Digital Converter


The Model 8701 ADC is a 100 MHz Wilkinson analog-todigital converter designed to provide a full 8192 channels of resolution in a wide range of applications. Its exceptional linearity improves peak shape and resolution, thereby improving the overall performance of your spectroscopy system.

Concentric Gain and Range controls together with digital Offset allow the user to maximize the use of limited MCA memory by selecting only a specific energy range of interest. This can be particularly useful for multi-input applications such as alpha spectroscopy, thus eliminating the need for analog bias amplifiers. These digital controls accomplish the same end more accurately and repeatably.

Conversion for the Pulse Height Analysis (PHA) mode can be initiated Automatically using an internal constant-fraction peak detector operating on the trailing edge of the input pulse, or can be Delayed up to 100 µs after the leading edge of the input pulse passes the input threshold. A front panel INSPEct test point is provided for monitoring the Linear Gate (LG), the time between the input threshold crossing and the beginning of conversion for either mode. Conversions may be enabled/disabled by COINCidence/ANTIcoincidence gating applied at any time during the Linear Gate interval.

Conversion for the Sampled Voltage Analysis (SVA) mode is initiated by the falling edge of a Gate pulse applied in the Coincidence mode. The same Lower and Upper Level Discriminators (LLD/ULD) limits are used for acceptance of the peak input during the positive gate time.

The Model 8701, provides front panel, screwdriver adjustable, multi-turn, potentiometers for the control of the LLD/ULD, as well as the ADC Zero.

The 8701 provides the connections required for use with current CANBERRA amplifiers that perform pileup rejection and live time correction (PUR/LTC). These ADC/amplifier interfaces are also required to use the Westphal loss free counting or precision live time techniques.2

The Model 8701 ADC is fully compatible with all current CANBERRA MCAs (with external ADC interface options such as the Model 556A), Digital Stabilizer and Analog Multiplexers.

Model 8701 Analog-to-Digital Converter


  • 100 MHz Wilkinson ADC
  • 8K channel resolution
  • Digital offset in 128 channel increments
  • Exceptional linearity (differential <±0.7%, integral <±0.025%)
  • Pulse Height Analysis (PHA) using either automatic peak detection or delayed triggering
  • Analog sample voltage analysis
  • Pulse pileup rejection and live time correction interfaces
  • Compatible with Loss Free Counting Systems1
  1. US patent 4,476,384.
  2. 2. G. P. Westphal, Nuclear Instruments and Methods 163 (1979) 189-196.