1 Introduction

What are Digital-to-Analog and Analog-to-Digital Converters?

DAC and ADC are interface devices where the conversion circuitry for ADC or DAC may be different.  These can be useful for various applications.  DAC can be thought of as a digitally controlled potentiometer.  The output produced is an analog (voltage or current) which is a normalized fraction of its full-scale setting.  The output, either voltage or current is dependent upon the reference value which is chosen and will determine the output.  If the reference value varies due to the analog signal, then the output is proportional to the product of the digital number and the analog input.  The product polarity is dependent upon the analog signal polarity, digital coding and conversion technique used.  In the case of ADC, the input is analog and the output is digital.  The digital output number is dependent upon the ratio of the quantized input to the full-scale reference.  If we consider a second analog input where the reference is allowed to change, then the digital output will be proportional to the ratio of the analog signal to the reference signal.   Furthermore, ADC can be thought of as a analog driver with a digital output.  Figure 1 and Figure 2, below depict a Digital-to-Analog converter and Analog-to-Digital converter, respectively. 

Figure 1. A Digital to Analog Converter will convert a digital signal to its analog equivalent.

Function: 

Vo - Analog output voltage 

Vref - Reference Voltage

N - Total number of bits of digital data permissible

       

                

Modes:

1. Conversion mode will convert a digital signal to analog.

2. Programmable gain amplifier mode is obtained when the signal is fed directly into Vref. In this mode the output is strictly analog, with no steps and the gain multiplier is in digital form.

Figure 2: Analog to Digital Converters will convert an analog signal to its digital equivalent.

        Function:

Vin - Analog input voltage

Vref - Reference voltage

N - Total number of bits of digital data

n - number of bits in the output

 Table 1: Show the converter interface characteristics