Name: 教授模擬電路中的截止頻率和有源低通濾波技術 (Teach Cutoff Frequency and Active Low Pass Filtering in Analog Circuits)
Uploaded: 2021-01-14T06:37:59.000Z
Duration: 4 min 51 s
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I'm Travis, and I'm an engineer on the academic team

And today I want to show you a new approach

to teaching frequency response calculations of filtering

As you know, active filters are very common building blocks

When a student is introduced to the concept for the very first

time, a single low pass op-amp filter, such as the one shown

here, is a good example to explain the circuit theory

and how to mathematically calculate the cutoff frequency.

However, when circuit complexity increases,

such as in the case of this third order low pass filter,

the theory becomes much more challenging.

in the same place is traditional coursework by using

I'll then force that theory with SPICE simulation and lab

So now I'm going to jump into a SPICE simulation circuit, where

I can build the same circuit with SPICE models of industry

standard parts commonly used in professional designs.

Here I'm using multisim as my SPICE simulator.

I'm going to go ahead and open my three stage low pass filter.

that allow me to quickly evaluate the circuit behavior

and experiment with an infinite number of scenarios.

Iterating different component values, circuit topologies,

and different types of op-amp SPICE models.

Over here I have a function generator generating

a sinusoidal input, and I also have an oscilloscope

to the input and the output of this circuit.

Now if I go ahead and run the simulation,

that we get that output bode plot of this three

Let me go ahead and stop this simulation.

In this case, I'm going to use the NI Elvis

II, which seamlessly integrates with this multisim environment.

that shows the three stages here with their three cutoff

Now our Elvis board allows us to blow out

and read back that signal with an oscilloscope

the same way we did in the multisim environment.

So here, I'll just go ahead and choose the actual Elvis device

And I'll make this stimulus channel-- or the channel

I'm going to look at for the signal I'm providing-- the AI0.

Then I'm going to make the response channel AI1.

And this is going to look at one of the stages of our low pass

I'm going to go ahead and allow real data to overlay

we have a low pass filter characteristic.

But it's roll off is nowhere near our simulated data.

But that's because we're looking at one stage.

Now let's look at the response channel AI2

I'm going to go ahead and run that again.

is getting a little bit closer to what our simulated data had.

So I'm going to go ahead and add in that third stage

by looking at AI channel three and running our simulation

matches very closely to the simulated data.

Now we can ask questions like, why doesn't it match exactly?

So we just finished looking at a three stage low pass filter

in not only the textbook, but in simulation and hardware.

For students, this experience of going from theory

to simulation, and then to actual interaction

with the circuits, leads to a much deeper comprehension

To further explore this approach to teaching analog circuits,

download the free courseware linked on this page.

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教授模擬電路中的截止頻率和有源低通濾波技術 (Teach Cutoff Frequency and Active Low Pass Filtering in Analog Circuits)

approach

concept

multiple

comprehension