Removing DC Offset: CS Research Project | 10Hz Sine Wave on +1V DC

[DefaultName]

Homework Statement

I need to remove a DC offset as apart of my research project I'm doing for my CS professor and his research group.

This signal is a sine wave, 10 Hz, riding on a +1V DC offset.

Homework Equations

I'm utilizing a high-pass filter using a series RC.

f = 1 / 2*pi*R*C - this is the cutoff frequency (ideal). I realize that practical filters do not cutoff exactly at this frequency, rather over a range of frequency.

The Attempt at a Solution

Input = 10sin(10t) + 1V = x(t)

So, I know that DC is 0 Hz.

Through my research, it seems that choosing the proper R and C values (close to the standard element values that you can buy from an electronics store), it would make sense that to block a 0 Hz signal, you "ideally" need to design the filter so the cutoff frequency is > 0 Hz. However, for practical and lab purposes, what frequency should I select as the 'cutoff frequency'? Do I select a random frequency above 0 Hz, with some room for leeway? I know that it will block it, but is there some sort of "rule" I must follow as to choosing the proper cutoff frequency?

As of now, I could say f = 1 / 2 * pi * R * C.

f = 5 Hz (Ill choose this)
C = 0.1uF
therefore, R = 318kOhm. The closest standard R value is 31.6kOhm.

Is this a good approach?

---

Also, is there a difference in using a simple series RC circuit or a differentiator high pass circuit? I know the gain is modified (inverted), but if I take care of that, is there any *real* advantage of using one?

My connections would be:

Vin -- C -- R -- Inverting Input
GND -- Noninverting Input
Output feedback --- Resistor --- Inverting Pin
and power supply for the OpAmp.

 

[CEL]

Homework Statement

I need to remove a DC offset as apart of my research project I'm doing for my CS professor and his research group.

This signal is a sine wave, 10 Hz, riding on a +1V DC offset.

Homework Equations

I'm utilizing a high-pass filter using a series RC.

f = 1 / 2*pi*R*C - this is the cutoff frequency (ideal). I realize that practical filters do not cutoff exactly at this frequency, rather over a range of frequency.

The Attempt at a Solution

Input = 10sin(10t) + 1V = x(t)

So, I know that DC is 0 Hz.

Through my research, it seems that choosing the proper R and C values (close to the standard element values that you can buy from an electronics store), it would make sense that to block a 0 Hz signal, you "ideally" need to design the filter so the cutoff frequency is > 0 Hz. However, for practical and lab purposes, what frequency should I select as the 'cutoff frequency'? Do I select a random frequency above 0 Hz, with some room for leeway? I know that it will block it, but is there some sort of "rule" I must follow as to choosing the proper cutoff frequency?

As of now, I could say f = 1 / 2 * pi * R * C.

f = 5 Hz (Ill choose this)
C = 0.1uF
therefore, R = 318kOhm. The closest standard R value is 31.6kOhm.

Is this a good approach?

---

Also, is there a difference in using a simple series RC circuit or a differentiator high pass circuit? I know the gain is modified (inverted), but if I take care of that, is there any *real* advantage of using one?

My connections would be:

Vin -- C -- R -- Inverting Input
GND -- Noninverting Input
Output feedback --- Resistor --- Inverting Pin
and power supply for the OpAmp.

Any capacitor will block DC. The requirement for the cutoff frequency of your filter is that it should be much less then the frequency of the signal you want to keep, so you should ideally use 1 Hz for your cutoff frequency.
By the way, you should use rd/s instead of Hz in specifying your signal. It should be:
Input = 10sin(2\pi\times10t) + 1V = x(t)
and not as you wrote.

 

[piercas]

I would suggest using a more rigorous approach to choosing the cutoff frequency for your high-pass filter. Instead of just selecting a random frequency, you should consider the frequency range of your signal and choose a cutoff frequency that is significantly higher than the highest frequency in your signal. This will ensure that the DC offset is effectively removed without affecting your signal of interest.

In terms of choosing the components for your filter, it is important to consider the trade-off between using standard values and achieving the desired cutoff frequency. In this case, it may be better to use a combination of standard values for R and C that give you a slightly higher cutoff frequency, rather than using a non-standard value for R that gives you the exact cutoff frequency you want. This will also help to minimize any errors introduced by the non-ideal behavior of the components.

Regarding the use of a simple series RC circuit versus a differentiator high pass circuit, it really depends on your specific application and the characteristics of your signal. A differentiator circuit may provide better performance in terms of filtering out the DC offset, but it may also introduce more noise or distortion to your signal. It is important to carefully analyze the trade-offs and choose the circuit that best suits your needs.

In summary, as a scientist, I would recommend taking a more systematic and rigorous approach to designing and implementing your high-pass filter to ensure the best results for your research project.