Electronics Engineering Magazine

Thursday, July 16, 2009

Mixed Electronic Designs

Analog Designs have to handle Linear Signals, Like 2.03 V and 35.3812 mA. Waveforms of all shapes from Straight Line DC Levels to the Jittery and Multi-Frequency Audio Waveforms.

Digital Designs manage Digital Signals, Like 0 and 5V Logic levels. All families of digital Logic, have some Threshold Limits and Voltage windows to determine Data Voltage or Current levels over Noise; this (Analog) comparator like action evaluates a High or Low Logic state. There are only two states, one is Low and the Other is High. 0 and 1 Respectively. The Third State in the word like Tristate, is a floating high impedance for Bus sharing between devices.

I would like to understand Mixed Circuit Designs as any circuit made of Valves, Discretes or Chips; in which both Analog signals and Digital Signals are Used. That would make an Analog Mux a Mixed Circuit, so also a PLL and a VCO.

Mixed Design Example

This is a R-2R Digital to Analog Converter, It converts a byte (8 bit) to a analog value. It has 256 levels including zero. This can be used to convert a byte sent from a microcontroller to a analog value like say 1.51 V. At full scale, when all 8 bits are high calibrate to give 2.55 V then ever bit increment is 0.01V, 10mV steps.

Digital to Analog with R2R Ladder Network

Mixed Circuits Analog with Digital

Mixed Signal IC or ASIC are chips that are mainly Digital on the Core but have peripheral I/O within the chip to interface with the real world outside, over Analog Signals. Sensors and Actuators use signals in the analog language. The CPU with its Math Power, speaks Digital Words, its behavior thus can be patterned by a Software Program.
RF Microwave and Communication Chips; Power Electronic PWM Integrated Circuits are Specialized Niche Mixed Sub-Domains.

Therefore any Student of Robotics, Multimedia and Instrumentation, must be good at these Mixed Designs and a master of C Programming.

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Mixed and Interface Circuits

Mixed and Interface Circuits : 

Most of the sensor interface and instrument inputs are analog; even if it event based like a limit switch, analog circuit protection and signal conditioning is required before it reaches the level sensitive digital circuit blocks.

Starting with Schmitt triggers and to the VCO and A-D Converters, are grades of Mixed Circuits. I feel Comparators like LM339, Timers like the 555 and Phase Locked Loop PLL are fundamental mixed circuits as they have a analog voltage detection.

DSP and uC with built in A-D or D-A or even SOC are Public ASICs and Fall in the Embedded Systems Block. Public ASICs are not user specific, they can be branded, numbered and provided with Application notes for the use of the Design Departments of any firm. User Specific ASICs are custom built and have only an application with that manufacturer for a Specific Product type. This also protects the IP of Code and Device Design. Custom ASICs are limited to the Platform and Technologies for which they were designed. Then we have programmable and configurable chips other than uC for logic like PLD, CPLD, FPGA and SOC, there is even some talk of mixed or analog configurable chips.


It would be nice if they made a breadboard chip with 12 opamps, 24 comparators, Some PLD and a couple of uC. Then we certainly need software trimmable or tweakable Resistors and Trimpots. This is the Magnum Opus of EDA. A EDA Chip Printer may be coming soon ! (Affordable by small firms).

Read More - Mixed and Interface Circuits - delabs

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