Introduction to comparators-based nonlinear circuits under open loop and positive feedback configurations.
Comparators and operational amplifiers are very similar in design. However, operational amplifiers are usually operated under negative feedback configuration, whereas comparators are operated under positive feedback or no feedback (open loop). This is the reason that operational amplifiers are equipped with a compensating capacitor that prevents them from oscillating. This compensating capacitor also makes the operational amplifiers slower than comparators. Hence, even though one can use an operational amplifier as a comparator, the operational amplifier will react slower than a comparator.
Many comparators have been designed with an open collector output stage to allow the coupling of multiple outputs yielding a logical operation. In most operations, one needs to add a pullup resistor to generate the required outputs. The outputs of comparators are usually high or low (one can see it as a binary digital signal, with some OpAmps even offering TTL outputs). Just like in the case of operational amplifiers, the output may be 1 to 2 volts off the rails.
The LM series is associated with integrated circuits made by National Semiconductor. LM stands for linear monolithic, describing how the analog components were fabricated onto a single piece of silicon.
Differential comparators
Part number | Predecessor | Obsolete? | Description |
---|---|---|---|
LM306 | High speed differential comparator with strobes | ||
LM111 LM211 LM311 |
LM106 LM710 |
High speed differential comparator with strobes | |
LM119 LM219 LM319 |
High speed dual comparators | ||
LM139 LM239 LM339 LM2901 |
Quadruple wide supply range comparators | ||
LM160 LM360 |
μA760 | High speed comparator with complementary TTL outputs | |
LM161 LM361 |
only LM161 | High speed comparator with strobed complementary TTL outputs | |
LM193 LM293 LM393 LM2903 |
Dual wide supply range comparators | ||
LM397 | General purpose comparator with an input common mode that includes ground | ||
LM613 | Dual op-amps, dual comparators, and adjustable reference |
Design by simulating and building a level detector, a window detector and a power supply monitor using the components shown in the figures below as inspiration for other values that you decide and confirm through calculations, simulation, and realization.
S. Franco "Design with Operational Amplifiers and Analog Integrated Circuits", McGraw-Hill 1988. Chapter 8.
This is a sample of how one can build a level detector. It is up to the user to figure out how this circuit can be adapted to a concrete application, like a charging level, the flood level of a river, the maximum temperature that a system can handle, etc.
Build this circuit with your own choice of Zener diodes replacing D1 and V2 with appropriate Zener diodes and figure out what temperature will be exceeded based on a given choice of the setting of the potentiometer and based on the temperature-controlled Zener diode of your choice (replacing V2). Refer to the lecture notes for the evaluation of the appropriate components’ values.
Another application could be realized by replacing V2 with a water level detector, and based on the setting of the potentiometer, one can show that the LED will switch when the flood level is exceeded, or when the drought level is reached.
Build this window detector by replacing V2 and V3 with appropriate Zener diodes and confirm the thresholds of the window detector based on the choice of the diodes. Do not forget to protect those diodes with resistors that would limit the current in the diodes.
Design this supply monitor to make the LED turn ON if the voltage is either as close as possible inside the range 10V to 15V, or outside this range. Your choice.
Besides the usual circuit information, schematics, and other relevant information, discuss the reason for your choices, and how your choices were achieved in terms of calculations related to the components’ values, observation, comments, and which components are most important in the way they affect the specifications.
Introduction to Schmitt triggers with dual and single power supplies.
Design by simulating the two circuits presented in the lab section of this part of lab 2 using the components of your choice and confirm through calculations and simulation that your implementation will be viable.
S. Franco "Design with Operational Amplifiers and Analog Integrated Circuits", McGraw-Hill 1988. Chapter 8.
Equipment needed from the stockroom: scope probe, leads.
Based on the values of the resistors R1 and R2, the thresholds are
$$ V_T = ± {R_1 \over{R_1 + R_2}} V_{CC} $$Hence VT = ±4V
R3 is just a pullup resistor.
Build this circuit with your own choice of thresholds. Calculate, simulate, and measure the relevant parameters. Discuss any discrepancies that may result from the implementation.
Do not use the values of the resistors presented in Figure 2.2.3 Choose your own values, and confirm through calculations, simulation, and implementation that the circuit performs as required. If there are any discrepancies, discuss the reasons. Suggest one application for this circuit. In the design process, you are given the thresholds, and you would have had to choose the resistors that will satisfy the requirements.
In your reports, present an introduction to each circuit, the circuit, the steps involved in the choices you made, the simulation results, and the implementation. Discuss any difficulty you may have encountered, any steps in resolving problems, discussion of the results, and finally, a summary for part 2.
Design, simulate and implement a 4-level bargraph display driver similar to the LM3914, using 4 comparators, 4 sets of LEDs and current-limiting resistors, and hopefully a Zener diode and a protecting resistor to generator a level that is adequate representative of some application. Test your circuit, and show what levels are involved in the turning levels for each LED. You can test your circuit with a DC voltage source, but for extra credit you can show your design by including a voice signal through a microphone and appropriate interface, the signal generated by a source like a smart phone, or a voltage signal generated by a sensor.
In your reports, present an introduction to each circuit, the circuit, the steps involved in the choices you made, the simulation results, and the implementation. Discuss any difficulty you may have encountered, any steps in resolving problems, discussion of the results, and finally, a summary for part 3, and finally a conclusion for the three parts.