FPGA-Based Relaxation D/A Converters With Parasitics-Induced Error Suppression and Digital Self-Calibration

In this paper, the implementation on a Field Programmable Gate Array (FPGA) of Relaxation Digital to Analog Converters (ReDACs), which take advantage of the impulse response of a first-order RC network to generate and combine binary weighted voltages, is addressed. For this purpose, the dominant ReDAC nonlinearity limitation related to the parasitics of the RC network is analyzed and a simple and robust technique for its effective suppression is proposed. Moreover, a ReDAC foreground digital calibration strategy suitable to FPGA implementation is introduced to tune the clock frequency of the converter, as requested for ReDAC operation. The novel error suppression technique and calibration strategy are finally implemented on a 13-bit, 514 S/s prototype (ReDAC1) and on a 11-bit, 10.5 kS/s prototype (ReDAC2), which are experimentally characterized under static and dynamic conditions. Measured results on ReDAC1 (ReDAC2) reveal 1.68 LSB (1.53 LSB) maximum INL, 1.54 LSB (1.0 LSB) maximum DNL, 76.4 dB (67.9 dB) THD, 79.7 dB (71.4 dB) SFDR and 71.3 dB (63.3 dB) SNDR, corresponding to 11.6 (10.2) effective bits (ENOB).