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Circuit Design and Examples. Design Guidelines Objectives Sensor Signal Conditioning Example Instrumentation Amplifiers AD620 OpAmps Op07 (modern) LM741 (ancient). Design Guidelines-1. Define the measurement objective

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Circuit design and examples l.jpg

Circuit Design and Examples

Design Guidelines



Signal Conditioning


Instrumentation Amplifiers



Op07 (modern)

LM741 (ancient)

Design guidelines 1 l.jpg
Design Guidelines-1

  • Define the measurement objective

    • Parameter: What do you need to measure: pressure, temperature, flow, level, etc

    • Range: What is the range of the measurements? 50-1500 F, 25-65 psi, 100-200 volts

    • Accuracy: What accuracy is desired and what specification of accuracy will be used? 5% of Full Scale or 2% of the reading.

    • Linearity: Must the measurement be linear?

    • Noise: How much noise is allowed?

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Sensor Definition in Engineering: the component of an instrument that converts

an input signal into a quantity that is measured by another part of the instrument

and changed into a useful signal for an information-gathering system.

Design Guidelines-2

A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.

  • Select the sensor/transducer

    • Parameters: What is the input and output of the transducer? E.g. pressure in resistance out, temperature in voltage out, light in current out

    • Transfer Function: Output/input relationship?

    • Time Response: 1st order, 2nd order?

    • Range: What is the possible range of sensor parameters? 0-1000C, 3-15 psi, etc

    • Power: What is the power specification of the sensor?

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Design Guidelines-3 instrument that converts

  • Analog Signal Conditioning

    • Parameter of output? Voltage, current, pressure, frequency

    • Range? 0-5V, 3-15psi, 4-20mA, 300-3500 Hz

    • Input impedance of the signal conditioning circuit? Many sensors require a specific impedance input or a range of allowable inputs

    • Output impedance to the next stage?

Example problem 2 33 in text my solution check the solution manual for the author s solution l.jpg
Example: Problem 2.33 in text instrument that convertsMy solution (check the solution manual for the author’s solution)

2.33: A bridge circuit has R1=R2=R3=120 ohms and V=10.0 volts. Design a signal conditioning system that provides an output of 0 to 5 volts as R4 varies from 120 to 140 ohms. Plot Vout vs R4. Evaluate the linearity

Desired output is VA-B




How to create a graph with a varying resistance l.jpg

  • Place a normal resistor as R4. instrument that converts

  • Double click on the value of the resistance

  • Enter {Rvar} [Yes the braces are required]

  • Go to “Get New Part” in the Draw Menu

  • Place the part name “PARAM” on the schematic page

  • Double click on Parameters

  • Enter Rvar as Name1

    • And Value1=100

How to create a graph with a varying resistance

  • Go to Analysis/Setup menu

  • Check and open the DC

    • Sweep box

  • Check Global Parameter and

    • Linear

  • Enter the Name of the variable

  • Which is Rvar here,

  • the start and end values of

  • the sweep and the increment

  • for the sweep

  • 12. Simulate





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V instrument that convertsA-VB



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V instrument that convertsA-VB

0 to .3846 to 0 to 5

Requires a gain of




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Need Differential Gain of 13 instrument that converts

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Instrumentation Amplifiers instrument that converts

Analog Devices Inc. is the largest supplier of instrumentation amplifiers in the world.

The AD620 is a low cost, high accuracy instrumentation amplifier which requires only one external resistor to set gains of 1 to 1000. Furthermore, the AD620 offers lower power (only 1.3 mA max supply current), making it a good fit for battery powered, portable (or remote) applications.

The AD620, with its high accuracy of 40 ppm maximum nonlinearity, low offset voltage of 50 µV max and offset drift of 0.6 µV/°C max, is ideal for use in precision data acquisition systems, such as weigh scales and transducer interfaces. The low noise, low input bias current, and low power of the AD620 also make it well suited for medical applications such as ECG and noninvasive blood pressure monitors.

The low input bias current of 1.0 nA max is made possible with the use of Superbeta processing in the input stage. The AD620 works well as a preamplifier due to its low input voltage noise of 9 nV/Hz at 1 kHz, 0.28 µV p-p in the 0.1 Hz to 10 Hz band, 0.1 pA/µHz input current noise. The AD620 is also well suited for multiplexed applications with its settling time of 15 µs to 0.01% and its cost is low enough to enable designs with one in amp per channel.

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AD620 Specifications instrument that converts

common-mode rejection ratio (CMRR): The ratio of the common-mode interference voltage at the input of a circuit, to the corresponding interference voltage at the output.

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Make vs. Buy: A Typical Bridge Application Error Budget instrument that converts

The AD620 offers improved performance over “homebrew” three op amp IA designs, along with smaller size, fewer components and lower supply current. In the typical application, a gain of 100 is required to amplify a bridge output of 20 mV full scale over the industrial temperature range of –40°C to +85°C.

Regardless of the system in which it is being used, the AD620 provides greater accuracy, and at low power and price.

Note that for the homebrew circuit, the OP07 specifications for input voltage offset and noise have been multiplied by 2, because a three op amp type in-amp has two op amps at its inputs.

AD620 vs opamp

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Error Budget instrument that converts

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Op07 vs LM741 instrument that converts

  • The OP-07 has very low input offset voltage (25µV max for OP-07A) which is obtained by trimming at the wafer stage. These low offset voltages generally eliminate any need for external nulling. The OP-07 also features low input bias current (±2nA for OP-07A) and high open-loop gain (300V/mV for the OP-07A). The low offsets and high open-loop gain make the OP-07 particularly useful for high-gain instrumentation applications.

  • The wide input voltage range of ±13V minimum combined with the high CMRR of 110dB (OP-07A) and high input impedance provides high accuracy in the non-inverting circuit configuration. Excellent linearity and gain accuracy can be maintained even at high closed-loop gains.

  • The OP-07 is available in five standard performance grades.

The LM741 series are general purpose operational amplifiers which feature improved performance over industry standards like the LM709. They are direct, plug-in replacements for the 709C, LM201, MC1439 and 748 in most applications.

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Op07 vs 741 instrument that converts

$1.25 for one Op07

25 for $25

$0.44 for one LM741

25 for $8

From Digikey

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Summary instrument that converts

  • Design Guidelines

    • Objectives

    • Sensor

    • Signal Conditioning

  • Example

  • Instrumentation Amplifiers

    • AD620

  • OpAmps

    • Op07 (modern) from Texas Instruments, Linear Technology, or Maxim

    • LM741 (old but useful) from National Semiconductor

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Digital Signal Conditioning instrument that converts

AC Bridges

Number systems

Boolean Algebra Example

Tristate Buffers

Comparators and Circuits

Schmidt Trigger

Window Detector

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AC Bridge Circuits instrument that converts

Generalized AC Bridge



Balanced when:

Z1Zx = Z2Z3

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Wien Bridge instrument that converts

Condition for Balanced Bridge







Wien bridge oscillator circuit http niuhep physics niu edu eads phys475 lab9 html l.jpg
Wien Bridge Oscillator Circuit instrument that converts

.001 uF



.001 uF

Expected Sine Wave

Frequency=15.9 KHz

Adjust the 50K resistor

for a sine wave output

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AC Bridges instrument that converts

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Number Systems instrument that converts

BITSA bit is the smallest element of information used by a computer. A bit holds ONE of TWO possible values: 0 meaning Off/False/NotSet and 1 meaning On/True/Set

Boolean Values

Boolean algebra recognizes True and False. So a single bit can represent a Boolean variable.

NIBBLEA nibble is a group of FOUR bits. This gives a maximum number of 16 possible different values. 2 ^ 4 = 16

LSB and MSB:The Least Significant Bit (LSB) is always drawn at the extreme right and has the least value and the Most Significant Bit (MSB) is always shown on the extreme left, and is the bit with the greatest value.

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Number Systems instrument that converts

BYTESBytes are a grouping of 8 bits. This comprises TWO nibbles.

Binary Coded Decimal [BCD]Binary code decimal digits (0-9) are represented using FOUR bits. The valid combinations of bits and their respective values are 0000 through 1001 with the binary combinations 1010 to 1111 not used.

If the computer stores one BCD digit per byte, its called normal BCD. The unused nibble may be all 0's or all 1's.

Packed BCD:

If two BCD digits are stored per byte, its called Packed BCD. This occurs in data transmission where numbers are being transmitted over a communications link. Packed BCD reduces the amount of time spent transmitting the numbers, as each data byte transmitted results in the sending of two BCD digits.

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Number Systems instrument that convertsHexadecimal

Refers to the base-16 number system, which consists of 16 unique symbols: the numbers 0 to 9 and the letters A to F. e.g. decimal 15 is represented as F in hexadecimal. This is useful because it can represent a byte (8 bits) as two hexadecimal digits. It is easier to read hexadecimal numbers than binary numbers.

To convert a value from hexadecimal to binary, translate each hexadecimal digit into its 4-bit binary equivalent. Hexadecimal numbers have either an 0x prefix or an h suffix. For example, the hexadecimal number 0x3F7A translates to the following binary number: 0011 1111 0111 1010

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Multiplication/Division instrument that converts

  • Multiplication by 10: Shifting left in decimal multiplies by 10. E.g. 05010 50010

  • Multiplication by 2: Shifting left in binary multiplies by 2. E.g. 01002 10002 which translates to 410 810

  • Division works the same way in that shifting right divides by 10 in decimal, 2 in binary, 8 in octal, and 16 in hexadecimal.

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Push-On Push-Off Control Circuit instrument that converts


24 volt dc


Relay Coil



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Example instrument that converts

Wt Sensor


IR Sensor


Robot Welder





A + B










C + D

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Tri-state Buffers instrument that converts




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Comparators instrument that converts


National Semiconductor

Texas Instruments


Fairchild Semiconductor

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National Semiconductor LM111 Comparator: instrument that converts(LM311 is $0.52 each at Digikey)

Open-drain outputs are outputs which at any given time are either actively sinking current (i.e., low voltage, typically considered logic 0) or are high impedance, but which never source current (high voltage, logic 1). Open-drain refers to the drain terminal of a MOS FET transistor. The equivalent concept on a bipolar device is called open-collector.

Article on the meaning of Rail-to-rail

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Comparator Circuit instrument that converts



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Zero Crossing Detector instrument that converts

LM339 is $0.52 at Digikey

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Schmidt Trigger Circuit instrument that converts

100 Hz Sinusoid

2.5 +2.5Sin(2π*100*t)

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Schmidt Trigger instrument that converts

Switches Low

Switches High

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Window Detector instrument that converts

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Summary instrument that converts

  • AC Bridges

  • Number systems

  • Boolean Algebra Example

  • Tristate Buffers

  • Comparators and Circuits

  • Schmidt Trigger

  • Window Detector