I need a 24-bit ADC with no internal low-pass filter

[hkBattousai]

I have been searching a 24-bit ADC in Farnell. All the result are for audio systems, they have internal high pass filter to eliminate DC component of the signal to be digitalized. However, I need an ADC which must be able to convert signals with DC component.

Required features:
1) 24-bit resolution.
2) 0-5V input signal range.
3) At least 1KSPS process rate.
4) Low cost.
5) Able to process base-band (0-1kHz range).

Can have either series or parallel output.
May not have internal oscillator.
Can have internal low-pass filter, but no HPF.

 

[Roff]

I have been searching a 24-bit ADC in Farnell. All the result are for audio systems, they have internal high pass filter to eliminate DC component of the signal to be digitalized. However, I need an ADC which must be able to convert signals with DC component.

Required features:
1) 24-bit resolution.
2) 0-5V input signal range.
3) At least 1KSPS process rate.
4) Low cost.
5) Able to process base-band (1-1kHz range).

Can have either series or parallel output.
May not have internal oscillator.
Can have internal high-pass filter, but no LPF.

You seem to be contradicting yourself. You said:

convert signals with DC component

Then you said:

1-1kHz range

But this implies no DC.

Can have internal high-pass filter

But a HPF cannot pass DC. Perhaps you meant "with no highpass filter"?

Do you need DC response, or not?

 

[hkBattousai]

I'm sorry, I don't believe I made so much mistake in my post.
I have corrected the mistakes, please help me find an IC satisfying my requirements.

Thanks in advance.

 

[blueroomelectronics]

The search function on the digikey site can narrow down your choices. It'll take some serious skill to get anywhere near 24 bits of resolution.

 

[Roff]

The search function on the digikey site can narrow down your choices. It'll take some serious skill to get anywhere near 24 bits of resolution.

5 volts at 24 bits is 300nV per bit. IMHO, that ain't gonna happen with 1kHz bandwidth.

 

[hkBattousai]

Then do you have any 16-bit ADC suggestion with the same features?

 

[Nigel Goodwin]

Exactly what are you wanting to do?.

 

[hkBattousai]

My purpose is sampling a 50Hz line voltage and detecting any external noise on it.

 

[Nigel Goodwin]

My purpose is sampling a 50Hz line voltage and detecting any external noise on it.

So why are you looking for silly high resolutions?, 10 bit or even 8 bit is all that you need - by the time you get to 16 bit layout is crucial, and it's difficult to get 16 bits of resolution.

I would suggest using a PIC for the job, and it's internal 10 bit ADC - 10 bits gives roughly 0.1% resolution.

 

[hkBattousai]

So why are you looking for silly high resolutions?, 10 bit or even 8 bit is all that you need - by the time you get to 16 bit layout is crucial, and it's difficult to get 16 bits of resolution.

I would suggest using a PIC for the job, and it's internal 10 bit ADC - 10 bits gives roughly 0.1% resolution.

Yes I'm planning to use PIC for this project.
I want to design my project as sensitive as possible. Can you please suggest me a 16-bit ADC; not for only this project for a general solution, for keeping in my mind just in case.

 

[Nigel Goodwin]

Yes I'm planning to use PIC for this project.
I want to design my project as sensitive as possible. Can you please suggest me a 16-bit ADC; not for only this project for a general solution, for keeping in my mind just in case.

As you're planning using a PIC, then do it initially with the internal ADC, and see how that works - you can then try a 16 bit one later, and see if it's any better (personally I'm sceptical). I've never used a 16 bit ADC, as I don't make PCB's there's not really much point - even 16 bit requires extremely well designed (and probably double-sided) layouts to try and get full resolution.

 

[hkBattousai]

As you're planning using a PIC, then do it initially with the internal ADC, and see how that works - you can then try a 16 bit one later, and see if it's any better (personally I'm sceptical). I've never used a 16 bit ADC, as I don't make PCB's there's not really much point - even 16 bit requires extremely well designed (and probably double-sided) layouts to try and get full resolution.

I used internal ADC of PIC18F2550 before (12-bit). I used it to convert temperature read from a LM35 IC to write it on a GLCD (WG12864B). It doesn't have enough resolution, its sensitivity was about ±0.5C. I need more resolution that that of PIC ADC has.

 

[Nigel Goodwin]

I used internal ADC of PIC18F2550 before (12-bit). I used it to convert temperature read from a LM35 IC to write it on a GLCD (WG12864B). It doesn't have enough resolution, its sensitivity was about ±0.5C. I need more resolution that that of PIC ADC has.

You're going about it the wrong way, you scale the input with an opamp and feed that to the ADC. A 12 bit ADC at only 0.5 degrees per bit would cover over 2000 degrees.

 

[hkBattousai]

You're going about it the wrong way, you scale the input with an opamp and feed that to the ADC. A 12 bit ADC at only 0.5 degrees per bit would cover over 2000 degrees.

Yeah, one second thought, may be it was because of doing something wrong in float point calculation. Anyway, that project was for learning GLCD interface and ADC features of PIC. Now I need a very sensitive ADC, I want to track a very small signal modulated on the power transmission line. Please suggest me an ADC unit for this.

 

[Nigel Goodwin]

Yeah, one second thought, may be it was because of doing something wrong in float point calculation. Anyway, that project was for learning GLCD interface and ADC features of PIC. Now I need a very sensitive ADC, I want to track a very small signal modulated on the power transmission line. Please suggest me an ADC unit for this.

How small is 'very small' and how big is the 50Hz sinewave.

 

[hkBattousai]

Power signal is a sinusoidal with 311V peak and 50Hz frequency, and the signal to be detected is a voice signal which adds itself to the power signal, typically at millivolts level.

 

[Nigel Goodwin]

The difference in levels is far too much (do the maths!) - however, i'm sceptical about sending audio signals round the mains at all, never mind at millivolt levels. Assuming you're talking about intercom signals over the mains wiring it's sent as a modulated RF carrier, not as audio (which wouldn't work).

So exactly what is it you're doing, or trying to do?.