# General Electronic Queries

#### karunanithi_pricol

Joined Mar 13, 2006
19
Hi all
Can u people clarify the below mentioned queries?

1.If we have designed the low pass filter for the cut off frequency (ex. fc=10khz), also the noise has been occurred in the range of 10khz i.e. noise has some phase shift with required signal. How can we filter it?

2.Semiconductor materials, which have the property of PTC AND NTC.
(Positive Temperature Coefficient and Negative Temperature Coefficient)
How the electronics industry made this property?

3.Fourier Series: We know that all waves can be represented in terms of Sine and Cosine waves. Why cant we represent the waves in terms of?

*Square and saw tooth wave (or)
*Square and triangle wave

4.In Time domain, we can analyze Amplitude Vs Time,
In frequency domain, we can analyze Amplitude Vs Frequency.
For which domain we will analyze Amplitude Vs Time Vs Frequency?

Karuna

#### Papabravo

Joined Feb 24, 2006
18,834
I consider these questions to be a bit out of the ordinary, to the point of being marginally relevant, but here goes.

1. Filters work on the frequency of the input, not the phase. If the input and the noise have the same spectrum then you are stuck with the noise.

2. PTC and NTC are inherent properties of materials. To the extent they can be controlled in the alloy or doping process the combination of a large PTC with a small NTC produces a smaller positive PTC. I'm no expert on this, but it certainly is not magic.

3. What distinguishes sine and cosine waves from the others that you mention is continuity and differentiability. An ideal square wave is not continuous. The derivative of an ideal square wave is also not continuous. For an ideal sawtooth or an ideal triangle wave they may be continuous, but they are not differentiable. These requirements on functions are essential the the properties discovered by Fourrier and others. OK, you say lets consider non-ideal waveforms and I say how can you describe them mathematically? The sine wave is completely defined by three parameters: the frequency, the amplitude, and the phase. For the square, sawtooth, and triangle, besides those three, we need aditional parameters to describe the slopes and the shape of the corners and peaks. You can see that the situation becomes rapidly intractable.

4. Thinking and analysis in 3 dimensions is incredibly hard. I've never seen any work on, or insight from an amplitude versus time versus frequency model. Perhaps you could provide some.

#### Murod

Joined Dec 24, 2005
30
karunanithi_pricol said:
4.In Time domain, we can analyze Amplitude Vs Time,
In frequency domain, we can analyze Amplitude Vs Frequency.
For which domain we will analyze Amplitude Vs Time Vs Frequency?

Karuna
It's difficult to make such kind of analysis with ideal approach. We can do that in an arbitrary time-domain, short time frequency analysis. You analyze the signal of a short time-slice around a point of time, then present the frequency spectrum for that point. So from a point to the the next point in the time domain, their frequency analysis are actualy taken from overlaped time slices. Look at spectrum analyzer, they can display the frequency content (frequency vs amplitude) from time to time. You can record it in 3D format.

Best Regards,

Hasan Murod.

#### etudionte

Joined Feb 20, 2007
1
Anwer to question no3:
We need a fundamental waveform to represent any periodic waveform. Sinusoidal waves fit the bill. Moreover..square and triangular waves are differentialderivatives of Sine-cosine waves. Hence rendered complicated in breaking up other periodic functions. .....