Analog to digital converter

Abstract

An analog-to-digital converter, finding particular application in a multichannel pulse height analyzer, includes means for digitizing the analog input in two conversion steps. To digitize the input to 13 bits, a 7-bit digital to analog converter (DAC) with a 7-bit up-down counter is used. During the first conversion step which is a coarse conversion, the input, V.sub.I, is compared with the DAC output, V.sub.L and the 7-bits of the counter are set by successive approximation. Thereafter, after settling, the DAC output is driven twice toward V.sub.I. The output of an amplifier of a gain 2.sup.7 is stored after each change of the DAC in one of two storage and hold circuits, depending on the polarity of the amplifier output. Then, the content of the 7-bit counter is transferred to the 7 higher order bits of a 14-bit buffer counter. Then, the fine conversion step is performed by successive approximation. In it the voltage in one of the storage and hold circuits is applied as the input and the difference of the voltages in the two storage and hold circuits is applied to a resistor ladder of the DAC. Then, the 7 bits of the counter are transferred to the 7 lower bits of the buffer counter. Thereafter, it is incremented by one and truncated by one, so that only its 13 higher order bits are read out, as the 13 bit output.