Dual reference voltage buffer and method for updating CDAC bit capacitors

DETAILED DESCRIPTION Accordingly, it is an object of the invention to provide a precision reference voltage circuit that avoids instability caused by a large peak current supplied to a load.
It is another object of the invention to provide a higher conversion rate in a successive approximation analog-to-digital converter utilizing an internal CDAC.
It is another object of the invention to prevent the conversion speed of a successive approximation analog-to-digital converter from being limited by instability in a reference voltage buffer.
It is another object of the invention to reduce RFI caused by large fast current spikes produced during a successive approximation process in a successive approximation analog-to-digital converter.
It is another object of the invention to provide a precision reference voltage circuit that is relatively insensitive to parasitic resistances and inductances during charging of a CDAC array capacitance to a reference voltage (or discharging it to a ground reference voltage).
Briefly described, and in accordance with one embodiment thereof, the invention provides a circuit and method for producing a stable reference voltage, by providing a circuit (27) that produces a reference voltage (VREFIN) on a first conductor (25), a buffer circuit (12) coupled to the first conductor (25) and producing a stable reference voltage on a second conductor (16), the buffer circuit 12 including an amplifier circuit (13) having an inverting input (-), a non-inverting input (+) coupled to the first conductor (25), and an output coupled to a third conductor (11), a first buffer circuit (13B) having an input coupled to the third conductor (11) and an output coupled by a fourth conductor (14) to the inverting input (-), the buffer circuit 12 also including a second buffer circuit (18) having an output (20) coupled to the second conductor (16) and an input coupled to the third conductor (11).
In a described embodiment, the reference voltage is a CDAC reference voltage in a successive approximation analog-to-digital converter