| 摘要 |
The single reference voltage system for A/D portion of CODEC includes an input lead connected to an operational amplifier (16), a signal switch (36) connected between the amplifier output and the top plates of a capacitive array (40) and a comparator (32) having an input connected to these top plates, another input connected to ground and an output connected to control logic (30). The circuit also includes a tapped resistor ladder (54) having N resistors connected in series and (N+1) nodes, one end of the ladder being connected to ground and the other end being connected to receive a single reference voltage. A switching arrangement (42,57) is provided for switching the bottom plates of the capacitor array to either ground, the reference voltage or one of the nodes on the resistive ladder. The control logic manipulates the signal switch and the switching arrangement so as to zero the top plate of each capacitor selectively determining a digital representation of a measured analog input signal. |
