Mixed Signal Circuits

Created: May/2020Last updated: 05/13/2020


Mixed signal circuits brings both analog and digital functionality under one circuit/chip (e.g. integrated circuit). it is commonly used to convert information from analog world to digital world, and vice versa such as on sensors and transducers.


Mixed signal circuit: a circuit that contains both analog and digital circuits on the same chip (integrated circuit).


ADC Process (Sampling ->Quantization-> Encoding/Conversion)

Dynamic Range

Linearity error


Differential non-linearity (DNL) reports the deviation in step size between actual analog input and ideal step size,1 LSB. ADC datasheet often report this as the maximum error per step.

Integral non-linearity (INL)  reports the deviation in ADC transfer function between actual curve to a straight line fit approximation using the end points of ADC actual curve. It's calculated as the difference between actual analog input transition edge and best fitted transition edge at each digital output transition. ADC datasheet report this as the maximum transfer function error.


Absolute/Maximum Error

Maximum deviation between actual curve and ideal ADC/DAC curve .

Alternative way to characterize Linearity



Common Architecture

Binary Weighted Resistor

R-2R Ladder

Digital Amplifier


CODEC (Encode and Decode)

In hardware world, CODEC a special hardware that contains both ADC and DAC functionalities that converts signal between analog to digital data stream and vice versa.

Note: Don't confuse this with  codec terms that is commonly heard as audio codec using in digital audio world. In software world, CODEC is a special software program that does encoding or decoding of a digital data stream between different data stream formats.

Example Design

Define the effective number of bit (ENOB) for a Digital MEMS Microphone


What reports the maximum measurement error for ADC and DAC?

For ADC and DAC, on datasheet, there is a absolute accuracy error (total error). This total error includes the non-zero offset, differences in slope (gain error), and quantization error that can be used on the single value error parameter for a quick evaluation.

Summary & Conclusion

Electronic system engineer must understand the fundamentals of mix signal circuits and apply them to highly digitized electronic system today. It's essential to make tradeoffs between sampling rate, precision, and cost in choosing a right mixed signal technology chip.

Further reading: