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Analog Design and Circuits

• Industrial Process Control Circuits
• Instrumentation and Measurement Circuits
  
• Mixed Circuits Analog with Digital
  
• Analog Op-Amp Circuits
  
• Temperature Measurement and Control

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Analog Electronic Design :

The very first designs that came about were analog designs, a Vacuum Tube amplifier is an example. Analog is the representation of data or physical parameter in an accurate and precise decimal number like + 72.182 mV. The greater the resolution required, the more demanding is the design for achieving  high accuracy and low drift. Digital circuits have only two voltage levels, high and low, the third state of floating, Hi-Z or high impedance is only for multiplexing or sharing a bus. This is done so that devices dont drive into each other and it is also used in external port drivers.

As an analogy, see the conventional water tap as an analog control, an electric light ON-OFF switch as a digital control.

Bob Pease - Analog Guru

Among the semiconductor products Bob designed are temperature-voltage frequency converters used in groundbreaking medical research expeditions to Mt. Everest in the 1980s. He also designed a seismic pre-amplifier chip used to measure lunar ground tremors in the US Apollo moon landing missions. Among his more memorable designs are the LM331 voltage to frequency converter and the LM337 adjustable voltage regulator. 

Even in digital, going from a low level say 0V to a high level say 5V is not instantaneous, the side of the square wave or the rising edge is not as straight as it looks. On zooming only the edge, you see that it is also an analog phenomena. The 'square wave' itself appears to be a summation of many sine waves, 'harmonics'.  This is because nature is analog, the sine wave is analog, the movements of the planets or even the spin of electrons in an atom too.

After the handheld Abacus calculator (low-power, durable, bio-degradable), Mechanical and electro-mechanical computers were made and studied, The very first electronic computers were Analog Computers using an opamp as a building block.

The Philbrick Archive and Operational Amplifier

Then came huge Digital Computers, Later LSI and other Microelectronic Innovations have precipitated handheld computers.

The Rising edge of the square wave depends on the Transient  Response of the devices, the slew rate and bandwidth too. Fast Op-Amps are required for many applications, in switching and also AC amplification. Beyond that, study goes into Power Electronics and RF-Microwave which are specialized extensions of Analog. Similarly study of Digital Circuits extends into Computers.

Have a look at Op Amp Applications Handbook

I have made some EE Analog Widgets, these are analog opamp tutors. Interactive Tutorial with Simulated Meters and Potentiometers, demonstrating how Operational Amplifier functions in different configurations.

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Analog Design Notes

(These are notes jotted down of my experience in the 90s, it may have spelling and other errors)

LM335 and LM336 - LM335 is a temp sensor, LM335 . use it for temp for CJC. Temperature Sensors - RTDs and Thermocouples in  Temperature Measurement. LM336-2.5 is an voltage Reference. precision 2.5V shunt regulator diodes, Applied as a precision 2.5V low voltage reference for digital voltmeters, power supplies or in opamp signal conditioning.

Schematics of delabs has many industrial instrumentation delabs designs using opamps.

Current Loop - 4-20 ma will drive DC drives, motors and steam valves. It is a current loop, for long distance transmission, current loop is not prone to noise and hum, EMI RFI. As it is a small power transmission no loss of data, also many equipments can be in one data loop. A single transmitter with 4-20mA out can drive a strip-chart recorder, motor, controller and SCADA input. all in a series loop. Current loop is like 4-20 mA

Opamp Notes and Types

• TL062, LF353, TL072, fet input. 1 tera ohm input imp.
• OP07 higher price, 1 giga ohm. 75uV offset.
• LF353 pin to pin replacement of TL062-72 and 82.
• LM358 works on single supply too, low price, inp imp 1 meg.
• LM324 Quad, works of batteries well.
• All work best with dual +/- 5 V or more. LM7805 -LM 7905.

Examine the operation of the following circuits of operational amplifiers: inverting amplifier, summing amplifier, difference amplifier, differentiator, and integrator.

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Points to Note -

• Analog ground (opamps), digital ground (CMOS) and power ground (relays and LED) should be separate, (linked at root)
• Glass epoxy PCB have high insulation resistance, above 10 tera ohms, and are not hygroscopic which means they do not drink water vapor, this makes them very suitable for precision instrumentation and sensitive circuits.
• When you measure DC levels in 16bit accuracy or more you need resistors which have temp. coeff. of 10ppm, or you may have to put the entire circuit in a stable 45 deg oven. Thermoelectric effects, EMI, RFI, pA Leakage currents, ground loops, contact resistance all can make the readings drift and unusable.
• High impedance points of circuit like 500 kilo ohm and above can pick up AC noise and DC leakage currents. this will affect the performance of circuit, so for DC you have to put a guard ring of the signal ground around that point in PCB. For RF you have to shield with things related to iron and mu metal, for low signals even a copper shield will do.
• Percentage and ppm: when percentage becomes like 0.001% it is difficult to manage, so we use ppm-parts per million.5% means 5 parts in 100 parts. 23 ppm means 23 parts per million parts. 0.001% - shift the dp-decimal point four places to right it is 10ppm. 0.01% is 100ppm which is the variation of value of mfr resistors on temperature change.

Related Sections

1. Circuits using only  discrete devices
2. Build a DMM or digital multi meter
3. Analog Interface for PC Ports
4. Design of a Constant Current Source
5. Precision Amplifier with Digital Control
6. Precision Attenuator with Digital Control