Capacitive DAC structure
View Patent ↗This application provides a novel capacitive DAC structure, which at least includes a fully differential DAC capacitor array, a comparator, and a sampling and holding switch provided between the fully differential DAC capacitor array and the comparator. In this application, by providing the sampling and holding switch, including a first logic switch, a second logic switch and a third logic switch, between the fully differential DAC capacitor array and the comparator, and changing the timing relationship of the switches to generate a stable common mode level Vcm, the area and power consumption can be greatly reduced, the IP competitiveness can be effectively improved, and it can be used for high-performance ADC design.
1 . A novel capacitive DAC structure, wherein the novel capacitive DAC structure at least comprises a fully differential DAC capacitor array, a comparator, and a sampling and holding switch provided between the fully differential DAC capacitor array and the comparator;
the fully differential DAC capacitor array comprises a first DAC capacitor array and a second DAC capacitor array, and the comparator comprises a first input level end and a second input level end;
the sampling and holding switch comprises a first logic switch, a second logic switch and a third logic switch, the first logic switch is provided between the first input level end and the second input level end, the second logic switch is provided between an upper electrode plate of the first DAC capacitor array and the first input level end, and the third logic switch is provided between an upper electrode plate of the second DAC capacitor array and the second input level end;
the first DAC capacitor array comprises a plurality of first capacitors, and upper electrode plates of the first capacitors are all connected to the second logic switch; the second DAC capacitor array comprises a plurality of second capacitors, and upper electrode plates of the second capacitors are all connected to the third logic switch;
the fully differential DAC capacitor array further comprises a plurality of first switches and a plurality of second switches, the first switches are connected to lower electrode plates of the first capacitors, the lower electrode plates of the two first capacitors with a capacitance value of C are connected to the same first switch, and the lower electrode plates of the other first capacitors are respectively connected to the respective first switches; the second switches are connected to lower electrode plates of the second capacitors, the lower electrode plates of the two second capacitors with a capacitance value of C are connected to the same second switch, and the lower electrode plates of the other second capacitors are respectively connected to the respective second switches.
2 . The novel capacitive DAC structure according to claim 1 , wherein the second logic switch is disconnected or selectively connected to a first reference level end or the first input level end; the third logic switch is disconnected or selectively connected to a second reference level end or the second input level end.
3 . The novel capacitive DAC structure according to claim 1 , wherein the first capacitors and the second capacitors are the same in parameters, and respectively comprise N+1 capacitors with capacitance values of C, C, 2C . . . 2 N-1 C, where Nis an integer.
4 . The novel capacitive DAC structure according to claim 3 , wherein a method for generating the common mode level by using the capacitive DAC structure comprises:
1) firstly, entering a sampling stage, connecting the first switches to a first input signal end, connecting the second switches to a second input signal end, disconnecting the first logic switch, connecting the second logic switch to the first reference level end, and connecting the third logic switch to the second reference level end;
2) then, closing the first logic switch, connecting the second logic switch to the first input level end, and connecting the third logic switch to the second input level end to obtain the stable common mode level.
5 . The novel capacitive DAC structure according to claim 3 , wherein the capacitive DAC structure comprises a 12-bit capacitive DAC structure.