Fig. 1 Functional Block Diagram
The ASNT7121-KMA is a 4-bit flash analog to digital converter (ADC) featuring high sampling rate and wide analog front-end bandwidth. The ADC system shown in Fig. 1 includes a linear input buffer (LIB) with a tree architecture and a CML-type input interface with internal 50Ohm single-ended terminations to vcc. The buffer delivers 15 matching copies of the input analog data signal dp/dn to the 4-bit flash ADC. The ADC creates 15 samples of the input data in thermometer code, which are then converted by a thermometer-to-binary encoder (TTB Encoder) into 4-bit binary words with a data rate f. The encoded data is demultiplexed into 16-bit wide words with a data rate f/4 and sent to the output through 16 low-power LVDS buffers. The output parallel interface can be aligned using a selectable PRBS generator that substitutes the encoded data with a test pattern. An optional digital-to-analog converter (DAC) can be used for the control of the ADC’s operation.
All operations are synchronized by the internal clock multiplication unit (CMU) based on a PLL (phase-locked loop) with an integrated divider. The block can operate in two different modes: clock multiplication (PLL is on) and clock division (PLL is off). In both modes, the divider generates internal clock signals divided by 2, 4, 8, and 16. The generated clocks divided by 4, 8, and 16 are sent to the LVDS output clop/n through a clock processor that selects the desired speed (cosel1, cosel2 control signals) and polarity (cosel3 control signal) of the output clock. In the second operational mode of CMU, the divider can be preset by the external signal res to ensure the correct phase relation between the output data and clock. The part operates from a single +3.5V power supply. All external control signals are compatible with the 2.5V CMOS interface.