LM311 – Voltage Comparator

The LM111, LM211 and LM311 are voltage comparators that have input currents nearly a thousand times lower than devices like the LM106 or LM710. They are also designed to operate over a wider range of supply voltages: from standard ±15V op amp supplies down to the single 5V supply used for IC logic.

LM311 – Voltage Comparator

LM311 - Voltage Comparator

Both the inputs and the outputs of the LM111, LM211 or the LM311 can be isolated from system ground, and the output can drive loads referred to ground, the positive supply or the negative supply. Offset balancing and strobe capability are provided and outputs can be wire ORed.

  • Operates from single 5V supply
  • Input current: 150 nA max. over temperature
  • Offset current: 20 nA max. over temperature
  • Differential input voltage range: ±30V
  • Power consumption: 135 mW at ±15V

Related Resources –

Voltage Comparator Information And Circuits

This page provides basic information about voltage comparator integrated circuits and is to act as reference material for other circuits. The circuits shown are based on the LM339 Quad Voltage Comparator chip or the LM393 Dual Voltage Comparator chip. These devices are functionally the same. The LM311 Voltage Comparator can be used for these applications as well but it also has a number of unique features.

Comparators and Schmitt Triggers

An LM311 in a comparator circuit is shown at the right, with the pin numbers for the connections. The open-collector output is at pin 7, and the ground for this transistor is at pin 1. It is shown pulled up to the logic voltage of +5 with a 1k resistor, which is typical. The output of the LM311 can sink 8 mA. A comparator’s output is essentially binary, YES or NO.


These devices consist of four independent voltage comparators that are designed to operate from a single power supply over a wide range of voltages. Operation from dual supplies also is possible, as long as the difference between the two supplies is 2 V to 36 V, and VCC is at least 1.5 V more positive than the input common-mode voltage.

Quad General Purpose Differential Comparator – LM339

An application from an old TI datasheet showing the versatility of this comparator. For me it was a workhorse and like LM324 was used in many products.

Quad General Purpose Differential Comparator - LM339
Current drain is independent of the supply voltage. The outputs can be connected to other open-collector outputs to achieve wired-AND relationships.

Differential to TTL convertor using LM339

  • Single Supply or Dual Supplies
  • Wide Range of Supply Voltage:
  • Low Supply-Current Drain Independent of Supply Voltage… 0.8 mA Typ
  • Low Input Bias Current …25 nA Typ
  • Low Input Offset Voltage . . . 2 mV Typ
  • Common-Mode Input Voltage Range Includes Ground
  • Differential Input Voltage Range Equal to Maximum-Rated Supply Voltage . . . ±36 V
  • Low Output Saturation Voltage
  • Output Compatible With TTL, MOS, and CMOS

Basic Analog for Digital Designers

“There is a long gap between engineering college and mid career in a non-engineering position, but technology marches on so a simple method of keeping abreast with the latest developments is required. This application note starts with an overview of the basic laws of physics, progresses through circuits 1 and 2, and explains op amp operation through the use of feedback principles.”

Basic Analog for Digital Designers – Application Note

Basic Analog for Digital Designers

AN9510.2 October 19, 2004 – This is an Analog Reference for the Embedded Engineer. An Application Note from Intersil Tech Reference.

  1. Basic Physics Laws, Circuit Theorems and Analysis
  2. Ohm’s and Kirchoff’s Laws
  3. Voltage and Current Dividers
  4. Thevenin’s and Norton’s Theorems
  5. Networks in the Feedback Path
  6. Types of Opamp Configurations
  7. Video Amplifiers


Some algebra, the basic laws of physics, and the basic circuit laws are adequate to gain an understanding of op amp circuits. By applying these tools to various circuit configurations it is possible to predict performance. Further in-depth knowledge is required to do op amp design, and there are many sources where this knowledge can be obtained. Don’t hesitate to try some of these tricks on your local circuit design engineer, but be aware that it may result in a long lecture about circuit design.

Integrated Device Technology – IDT – Semiconductors

Leadership in digital technologies, coupled with its in-house analog capabilities. They have solutions for Computing, Communications and Consumer Electronics. They Streamline data transmission and data-communication in the Networks.

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The Product Line includes Clock / Timing Devices , Display / Video Solutions, Memory Interface Products and SRAMs. For Small Computing devices there are Touch Products, Processors and USB/PCI Express Chips. They also manufacture RISCore 64-bit Processors for large computing systems.

Integrated Device Technology - IDT - Semiconductors

DAC1653Q-DB High-Performance 16-bit Quad DAC

“The DAC1653Q-DB evaluation board features the DAC1658Q high-speed quad channel 16-bit DAC with high common mode voltage. The DAC1653Q-DB evaluation board is suitable for dynamic performance evaluation from low to high output frequency configurations.”

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Design of a Constant Current Source

This article will explain the way a simple transistor based current source is designed, this will give an idea on how some components can be used in a practical way to make the circuit do some function, the objective is not design but to become familiar with the basic ideas.


We need a fixed current around 20mA for a voltage variation of 10V to 20V to drive a LED flasher circuit.

Component Selection. The transistor should handle 20V * 2 = 40V and a current of 20mA * 5 = 100mA. We have to overrate the components for long term reliability and make the design rugged. Chosen MPSA92 PNP-300V-500mA which is good for this job. Look at the pin details of MPSA92 in the bottom view given in the right of this page in its TO-92 package, it has a beta of 25 . The Power dissipation of MPSA92 can be upto 650mW , our requirement may be a max of 20V*20mA = 400mW which is just within limits.

Now we need a voltage reference a low cost voltage reference is a LED which has a 1.6V forward drop. As the circuit is a not an accurate one CFR 5% resistors are fine.

From my Tutorials on Basics and Instrumentation Electronics

Circuit design.

The LED at 40mW will last long, some energy emits as heat and some as light. 40mW / 1.6V = 25mA. so let us choose 20mA max LED current as a thumb rule.

In this circuit the LED is used as a reference so to keep it cool a 2.2K is chosen. (20V – 1.6V) / 2.2K = 8.3mA on the high side and when voltage is 10V the current will be 3.8mA min. .

You should know that the LED forward drop can change with ambient light as it is photo sensitive and will vary with temperature.

Look at the circuit in the right, the LED has a forward drop of 1.6V which is applied across the resistor R4 and the base-emitter diode. That means 1V across R4 as a diode drop is around 0.6V. The base-emmiter now gets forward biased and a small base current Ib flows . The Ic or collector current is 1V / 50E = 20mA. The Ib = Ic / beta, That means 20mA / 25 = 0.8mA which flows thru R4 and R5.

The Load Resistor R6 represents the LED flasher circuit that consumes 20mA, even on short circuit of R6 the current is limited to 20mA.

When more current flows in R6 the voltage at emitter falls, the voltage at base is 20V – 1.6V =18.4V, and the voltage at emitter should be 18.4 + 0.6V = 19V for bias and Ibto flow. When Ic increases the Ib reduces to that extent as only to maintain emitter voltage at 19V, this way Ic is kept constant, if Ic reduces the voltage at emitter builds up to rise Ibwhich in turn builds up Ic. so we made a current regulator.

Circuit Improvement.

The circuit can be improved by using a zener in place of the LED or better still a temperature compensated reference like LM336.

The circuit on the right will be more stable, but still the forward drop on base-emmiter junction is temperature sensitive. The base current will also introduce an error, so you can get a 8 bit stability, that means around 255 counts on an A-D converter. If you need a more stable current source you should design with FET and opamps.

LM336-2.5 pdf details, It has a 2.5V drop. A LM336-5.0 pdf version is also available for 5V. these are from National Semiconductor.

Operating Current of LM336 is 400uA to 10mA, 20V The max. voltage 20V / 3.3K = 6mA. so within limits. Then you can compute the rest, wire it up to see if your design works.

“If all parts are working, connected in proper polarities and there are no dry solders and loose connections then any circuit well designed ought to work. ”
Solderman 1702

anantha narayan delabs

Read more at Instrumentation and Measurement Circuits

DRS4 Evaluation Board – Paul Scherrer Institut

Ever wanted to develop a Professional High Speed DAQ or a Storage Oscilloscope or even a High Speed Communications grade Logic Analyzer. Here is a front end Analog Mixed Chip with Eval Board.

You could make a High Speed Test Instrument and probably build a tablet app front end. How would a 200 M Hz Oscilloscope look on you 10 inch tablet. You will float in the clouds. – delabs

The DRS chip is a full custom Integrated Circuit developed at PSI, Switzerland. It contains a switched capacitor array (SCA) with 1024 cells, capable of digitizing eight analog signals with high speed (6 GSPS) and high accuracy (11.5 bit SNR) on a single chip.

DRS4 Evaluation Board - Paul Scherrer Institut
DRS4 Evaluation Board – Paul Scherrer Institut

By using channel cascading, we can configure this board with 2048 bins for each channel at the expense of a lower analog bandwidth of about 500 MHz. The on-board comparators enables the board to do a self-triggering on a programmed level of any of the input channels or logical combination of channels, much like an oscilloscope.

Highlights of Board with One DRS4 chip

  • Four 50-Ohm terminated input channels with SMA connectors
  • Active input buffers which result in an analog bandwidth of 700 MHz (-3dB).
  • One AD9245 ADC to digitize signals from the DRS4 chip
  • One Xilinx Spartan 3 FPGA for readout control
  • A 16-bit DAC to generate all on-board control voltages
  • A serial EEPROM containing serial number and calibration information
  • Internal trigger with user-defined thresholds on any of the four channes.

Maxim Integrated – Analog Integration

They make unique and affordable semiconductor solutions in the areas or Analog and Mixed-signal. The digital and analog interface ICs are useful products in maxim for automotive and industrial product engineering.

Maxim Integrated – Analog Integration

They have Embedded Systems and Optical Communications in their Portfolio. They are well known for Power and Battery Management chips.

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Novato smart sensor transmitter. – 4-20mA Loop-Powered Temperature Sensor with HART

The Novato reference design is a 16-bit, high-accuracy, loop-powered temperature transducer that transmits temperature information from a remote object to the central control unit over a 4-20mA current loop and using the highway addressable remote transducer (HART) communication protocol.

 Novato smart sensor transmitter.

HART Communication Protocol

The Novato reference design fully satisfies the HART physical layer requirements. The HART functions set is developed by AB Tech Solution, an engineering firm specialized in product development services for industrial automation applications.

Established in 1983, Maxim Integrated Products is a worldwide leader in design, development, and manufacture of linear and mixed-signal integrated circuits (ICs).

Maxim circuits “connect” the real world and digital world by detecting, measuring, amplifying, and converting real-world signals, such as temperature, pressure, or sound, into the digital signals necessary for computer processing.

Maxim Integrated
160, Rio Robles, San Jose, CA 95134 USA.