| 摘要 |
In an analog to digital converter circuit for a CODEC a single reference voltage is used for comparing both positive and negative input signals. The circuit comprises a capacitor array to define the decision levels corresponding to the end points of companding elements with the top plates of all capacitors in the array being connected in parallel through a single switch from an incoming analog signal source and to one input of a comparator. The bottom plate of each capacitor is connected to one of a series of three-way switches, all of which have separate terminals connected to the output of a voltage reference, to separate switches on a linear resistor string connected to the voltage reference output, and to ground. All switches are controlled by control logic connected to the comparator output. Analog to digital conversion is achieved by zeroing the voltage on the top plate of a selected capacitor in the array when the voltage on its lower plate is manipulated by signals from the control logic operating the switches in the linear resistor string selectively. By properly sequencing the switching of capacitors in the array, a single reference voltage is used. |
