I love to hear any thoughts about a good break-before-make analog switch with low charge injection or even even better any thoughts on generating precision amplitude square waves in general. As to why ...
I have a 5V±5%/GND powered op amp (AD8648), a precision 2.5V(±0.2%) low impedance voltage, and an external 3.3V±5%/GND clock input that runs at about 10 KHz. I need to generate precision amplitude 10 KHz square waves that are symmetric about 2.5V. The amplitude will be controlled with a 10K digital potentiometer. The potentiometer resistance is known with 0.1% precision. The circuit needs to be as low cost as possible. Ideally, I need a precision of about 1mv for an amplitude of up to 2.5V±~1V. The resolution is not an issue as much as the precision. I plan to use the AD8528 64 tap potentiometer, since it comes calibrated with the 0.1% accurate full scale value stored in internal memory.
One possibility that I am considering is to scale the voltage across a precision 1V reference with the potentiometer and then use analog switches to switch a capacitor above and below the 2.5V common mode voltage. I have been looking at various analog switch possibilities and the best seems to be the LTC6943 switched capacitor controller, but it costs about $7 a pop. I could potentially use other analog switches, but I am worried about the voltage offset you can get from charge injection from a switch not made specifically to balance it out, like the LTC6943.
Below is the modified LTC6943 voltage inverter application circuit. It uses an inverting and non-inverting version of this circuit to drive the op amp input above and below the 2.5V reference by Vin, which will come from a digital pot divided version of the 1V reference.
So, to repeat the question, any thoughts about a good break-before-make analog switch with low charge injection or even any thoughts on generating precision amplitude square waves in general?