# Solving a Filter Problem with a Voltage Source Graph

• EvLer
In summary, the conversation revolved around a problem involving a magnitude graph of voltage and frequency, and a sketch of a circuit with a current source and voltage across it. The question was to determine the circuit and its values. The graph indicated a low-pass filter and the use of steady-state sinusoidal response and phasors was discussed. However, without the sketch, a solution was deemed impossible. The conversation also touched upon the use of Latex and the importance of providing precise and detailed information in problem postings.
EvLer
I have this filter problem,
I am given a magnitude graph (magnitude vs frequency, with a point on it) of voltage across input current source and a sketch of a circuit: black box connected with a current source (cos(wt) and voltage across it is Vmcos(wt + theta)) and the question is to figure out what's in the box and values. Looking at the graph, it is low-pass filter

So far we covered steady-state sinusoidal response and phasors. But all the examples in the book are with voltage sources so I am thrown off, I am not sure if I can do source transformation on it!

So, I tried getting ratio of v/i and using phasor e-notation, I got Vm*e^theta, so does that mean that since impedance has positive imaginary part, it's inductor and resistor in series? What would a point on the magnitude voltage graph give me?

Any hint on this would be GREATLY appreciated...

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Missing ?

The problem here is that a multitude of circuits may do the same thing
( you left off the sketch ) without which a solution is impossible .
However this sounds like Homework so I am not inclined to repy.
Ray.

rayjohn01 said:
The problem here is that a multitude of circuits may do the same thing ( you left off the sketch ) without which a solution is impossible .
However this sounds like Homework so I am not inclined to repy.
I do not know how to use Latex, so I described the graph as a graph of low-freq. filter: as w->infinity, |v| -> 0, since this is the only information that was provided for us.
I resolved it with a TA, but thanks for making me feel welcome. I did not hide it was a homework, and it wasn't like I did not make an effort in trying to understand this. I guess I had a wrong idea about the point of this forum: help people; but evidently students are not considered to be "people" by your standards.
No hard feelings.
Thanks for your time  and that other time you answered my question[/edit].

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Oh Ray is always like that... he's just kidding.

We know you tried it out --- but he has a point, I think I oculd help you out if you attach the pdf of which the plot is drawn. Or a link to your course webpage could be helpful!

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To Elver -- sorry I think I was a little tired. The point here is that exact info is required
i.e the graph shape matters. You say that you need to get what is in the box AND values . You can only do this in very simple cases which one may be able to judge by the shape of the graph. I assume (but do not know ) that the point is chosen to reveal
a value of loss at a specific frequency leading to values.
In electronics the circuit and graph info is vital --- I do not use Latex either --- I found that any drawing package which can produce a small Jpeg file can be used here
I happen to use Corel Draw Here is a sample of what it can do in a couple of minutes ( the Jpeg is at 55 dpi to keep it small ) .everything here is drawn or typed and placed . it's not a schematic package ).
I do not use BMP's because unless they are zipped they are too large -- and if they are zipped they cannot be viewed on the forum.
Ray

#### Attachments

• ciruit.jpg
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Oh, I did not expect you to go at such length
Actually that is exactly what the circuit is supposed to look like. Next time I will be more considerate when it comes to details and precision of the problem posting. The tip on drawing is very helpful.
Thanks!

To Theelectrichild --- Hey I am not ALWAYS like that ---- but the solution to a problem IS a GOOD Question . Ray.
But you are quite right about the kidding !
and thank you for keeping the discussion light hearted.

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## 1. What is a filter problem and how is it related to a voltage source graph?

A filter problem refers to the task of designing a circuit that can selectively pass or block certain frequencies of an input signal. A voltage source graph is a visual representation of the voltage output of a circuit over a range of frequencies. In solving a filter problem, the voltage source graph can help determine the effectiveness of the circuit in filtering out unwanted frequencies.

## 2. How do you approach solving a filter problem with a voltage source graph?

First, identify the desired frequency range to be passed or blocked by the filter. Then, choose the appropriate filter type (low-pass, high-pass, band-pass, etc.) based on the frequency range. Next, calculate the necessary component values (resistors, capacitors, etc.) using the filter's transfer function. Finally, plot the voltage source graph using the calculated values to determine if the filter meets the desired specifications.

## 3. What are some common difficulties in solving a filter problem with a voltage source graph?

One common difficulty is finding the right combination of component values to achieve the desired frequency response. This may require trial and error or using more complex circuit designs. Another challenge may arise from non-ideal components, which can lead to discrepancies between the calculated and actual voltage source graph.

## 4. How do you optimize a filter design using a voltage source graph?

To optimize a filter design, you can use simulation tools to adjust component values and see the resulting changes in the voltage source graph. Additionally, considering the trade-offs between different filter parameters (such as passband ripple and stopband attenuation) can help achieve the most efficient design for a specific application.

## 5. Are there any practical applications for solving filter problems with a voltage source graph?

Yes, filter design is crucial in many electronic systems. For example, in audio systems, filters are used to eliminate unwanted noise and improve sound quality. In communication systems, filters are used to separate different frequency signals and prevent interference. In power supplies, filters are used to smooth out the output voltage and reduce ripple. In summary, filter design is essential for achieving desired performance and functionality in various electronic applications.

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