Cheatography

# ADC and DAC Cheat Sheet (DRAFT) by raxxen5

This is a draft cheat sheet. It is a work in progress and is not finished yet.

### Digital to Analog Conversion

A digital to analog converter (DAC) converts a digital signal to an analog voltage or current output.

### Types of DAC

 Binary Weighted Resistor Utilizes a summing op-amp circuit Weighted resistors are used to distin­guish each bit from the most signif­icant to the least signif­icant Transi­stors are used to switch between Vref and ground (bit high or low) Assume Ideal Op-amp No current into op-amp Virtual ground at inverting input Vout= -IRf Pros Cons Simple Constr­uct­ion­/An­alysis Requires large range of resistors (2000:1 for 12-bit DAC) with necessary high precision for low resistors Fast Conversion Requires low switch resist­ances in transi­stors Can be expensive. Therefore, usually limited to 8-bit resolu­tion. R-2R Ladder If the bit is high, the corres­ponding switch is connected to the inverting input of the op-amp. If the bit is low, the corres­ponding switch is connected to ground. Pros Cons Only two resistor values (R and 2R) Lower conversion speed than binary weighted DAC Does not require high precision resistors

### Analog to Digital Conversion

It is an electronic process in which a contin­uously variable (analog) signal is changed, without altering its essential content, into a multi-­level (digital) signal.

### Resolution

The resolution of the converter indicates the number of discrete values it can produce over the range of analog values.

The resolution determines the magnitude of the quanti­zation error and therefore determines the maximum possible average signal to noise ratio for an ideal ADC

### ADC Value Calcul­ation

For an N-bit ADC, the digital repres­ent­ation depends on Number of Bits and Reference values

### Example

 Given a half wave input signal: x(t) = Acos(t), A = 5V Full scale measur­ement rang = 0 to 5 volts ADC resolution is 8 bits: 28 = 256 quanti­zation levels (codes) ADC voltage resolu­tion, Q = (5 V − 0 V) / 256 = 5 V / 256 ≈ 0.0195 V Q ≈ 19.5 mV.