Comparator

Behavioral model of a comparator integrated circuit

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Libraries:
Simscape / Electrical / Integrated Circuits

Description

The Comparator block is an abstracted behavioral model of a comparator integrated circuit. It does not model an internal transistor-level implementation. Therefore, the block runs quickly during simulation but retains the correct I/O behavior. The block models differential inputs electrically as having infinite resistance and a finite or zero capacitance.

The block models the gate output as a voltage source driving a series resistor and a capacitor that connects to ground. The output pin connects to the resistor-capacitor connection node. If the difference in the inputs is greater than the input threshold voltage, then the output is equal to the High level output voltage ($$V_{OH}$$). Otherwise, the output is equal to the Low level output voltage ($$V_{OL}$$).

The output model is shown in the following illustration.

Examples

Phase-Locked Loop

How to model a phase-locked loop. The charge pump and filter are modeled using discrete analog components whereas the oscillator is represented as behavioral component using the Simscape™ Electrical™ Voltage-Controlled Oscillator block. The D-type flip-flops in the phase detector are represented in a simplified form using Simulink® blocks to define the behavior, and electrical components are used just at the interface. Non-zero initial conditions are applied to C1 and C2 in order to start the VCO out of phase and test the tracking ability.

• Open Model

Assumptions and Limitations

Modeling of the output as a controlled voltage source is representative of a totem-pole or push-pull output stage. To model a device with an open-collector:

1. Connect the output pin to the base of an NPN Bipolar Transistor or PNP Bipolar Transistor block.

2. Set the Output resistance parameter to a suitable value.

Ports

Conserving

+ — Non-inverting input

electrical

Electrical conserving port associated with the comparator non-inverting input.

- — Inverting input

electrical

Electrical conserving port associated with the comparator inverting input.

OUT — Output port

electrical

Electrical conserving port associated with the comparator output

Parameters

Input

Input offset voltage — Input offset voltage

5 mV (default)

The voltage which the difference in the input voltages must be greater than so that the comparator gives a logic output 1.

Average input capacitance — Average input capacitance

0 pF (default)

You can usually find this capacitance value on a manufacturer datasheet. Setting this value to zero can result in faster simulation times.

Output

Low level output voltage — Low level output voltage

0 V (default)

The steady-state output voltage, $$V_{OL}$$, when the voltage difference across the inputs is less than or equal to the threshold voltage, and the output current is zero.

High level output voltage — High level output voltage

5 V (default)

The steady-state output voltage, $$V_{OH}$$, when the voltage difference across the inputs is greater than the threshold voltage, and the output current is zero.

Output resistance — Output resistance

50 Ohm (default)

This parameter is the ratio of output voltage drop to output current. Set this parameter to $(V_{OH}-V_{OH}{}_1)/I_{OH}{}_1$, where $V_{OH}{}_1$ is the reduced output high voltage when the output current is $I_{OH}{}_1$.

Propagation delay — Propagation delay

0 s (default)

Set this value based on the high-to-low and low-to-high propagation delays.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2009b