Analog Design and Circuits
Analog Electronic Design :
The very first designs that came about were analog
, 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
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.
Philbrick Archive and Operational Amplifier
Then came huge Digital Computers, Later LSI and other
Microelectronic Innovations have precipitated handheld
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
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.
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.
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
- 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.
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
- 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.
- Circuits using
only discrete devices
- Build a DMM or digital multi
- Analog Interface for PC Ports
- Design of a Constant
- Precision Amplifier
with Digital Control
- Precision Attenuator
with Digital Control