Data converter for directly providing outputs in two's complement code

In a data conversion system for receiving an analog input voltage and converting the received analog input voltage to a digital output in offset binary code, a method of changing digital code format of the data conversion system from offset binary code to two's complement code, comprising the steps of:

• receiving the input voltage;
• comparing the stored input voltage with a first reference voltage to provide an output sign bit of the digital output voltage;
• and
• selectively coupling first and second reference voltage terminals of the data conversion system between either a first pair of reference voltages or a second pair of reference voltages in response to the output sign bit, the first pair of reference voltages comprising a second reference voltage coupled to the first reference voltage terminal and the first reference voltage coupled to the second reference voltage terminal, and the second pair of reference voltages comprising the first reference voltage coupled to the first reference voltage terminal and a third reference voltage coupled to the second reference voltage terminal, said third reference voltage having a magnitude substantially equal to a magnitude of the first reference voltage and of opposite polarity to the first reference voltage.

In a capacitive data conversion system for selectively receiving an analog input voltage and storing the input voltage via a plurality of parallel coupled capacitors, a method of providing a digital output signal in two's complement code, comprising the steps of:

• comparing the stored input voltage with a predetermined first reference voltage to provide an output sign bit of the digital output signal;
• selectively coupling each of the capacitors to one of two reference voltage terminals, said first reference voltage terminal receiving either a second reference voltage or the first reference voltage while said second reference voltage terminal respectively receives the first reference voltage or a third reference voltage;
• and
• performing a successive approximation of the stored input voltage to provide the digital output signal in two's complement code.