Burr-brown Corporation

Andreas O Fees

A circuit for producing a stable CDAC reference voltage in a successive approximation analog-to-digital converter includes a circuit (27) producing an input reference voltage (VREFIN), and a buffer circuit (12) producing a stable reference voltage in response to the input reference voltage. The buffer circuit includes an amplifier (13) having a non-inverting input receiving the input reference voltage. A first buffer (13B) receives the output of the amplifier and produces output that is fed back to an inverting input of the amplifier. A second buffer (18) also receives the amplifier output. A first transistor switch (19) couples the output of the second buffer to a CDAC. A second transistor switch (29) couples the CDAC to ground. A third transistor switch (26) couples the first buffer to the CDAC. The first transistor switch (19) closes to cause an initial 'coarse' charging of a first capacitance of the CDAC by the second buffer (18). The third transistor switch (26) closes after the coarse charging to perform a final precise 'fine' charging of the first capacitance of the CDAC by the first buffer circuit (13B). Coarse and fine discharging of the CDAC to ground also are provided to increase accuracy of the analog-to-digital converter and to minimize RFI produced thereby.

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Neckartenzlingen, Germany

Andreas O Fees