16-bits ADC anyone?

Hi all,

I am working on a project where I need some 16 bits ADC to retrieve information from a sensor. I also need a small microcontroller such as a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5 (qty 1000), which is 5 times more expensive than the controller!

Does anyone have an idea about how I can get some low cost ADC- Controller solution? I need only few dozens of samples per second, so some of you may have nice tricks to do that (op-amps, capacitor charge time stuff and the like).

Thanks, Bruno

Reply to
Bruno Richard
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You might want to look at sigma-delta type converters. They often offer much better than 16 bits at ~100 Hz, and generally cheap.

Peter

Reply to
Peter Dickerson

Try something like the Silabs C8051F353R ? Shows as $3.48/1500 pcs at Digikey.

-jg

Reply to
Jim Granville

Bruno Richard brought next idea :

Take a look at BB ADS1100 that works 16bit @ 8SPS. It has I2C interface (just 3 bytes to retrieve HIGH/LOW word of converted value and the status register) and I think it's around 2/3 euros.

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Bye!

Reply to
djordj

The Texas Instruments MSP430 microcontroller has 16 bit ADC on chip. In quantity, it should be in the $3 to $5 range depending on which version you need. I think Analog Devices has 8051's with 16 bit ADC. You might also look at Maxim. I seem to recall that they have gotten into microcontrollers with high resolution ADCs.

Reply to
Gary Reichlinger

Seconded. You certainly want sigma-delta, and you certainly want ratiometric. This device does both in a rather nice package.

Steve

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Reply to
Steve at fivetrees

You might see what you can accomplish by using a cheap micro witha 12- bit ADC and a lot of careful filtering (averaging) in software, since your needed sample rate is quite low. It might not get you 16 real bits, but if unit cost is a driver, figuring out if the accuracy it can get you would be enough is probably worth the effort.

Reply to
cs_posting

In this vein, you may want to check the SiLABS application note AN11 called "IMPROVING ADC RESOLUTION BY OVERSAMPLING AND AVERAGING"

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Reply to
antedeluvian

Bruno Richard schrieb:

You can build a cheap & simple dual slope converter with an external reference (like TL431), MUX (4051), integrator and comparator (standard OP). With an 8051, you can generate the fixed integration time and measure the variable deintegration time with only one of the internal timers, while the signal from the comparator provides the timer gate signal and the EOC interrupt at the same time. (I don't know if other micros also have 16 bit timers with external gate signal that also can generate edge triggered interrupts without additional pin.)

With very cheap standard parts, we have made 15 bit ADCs this way. You also get line frequency suppression by proper selection of the integration time (we tend to use 100 ms to suppress both 50 Hz and 60 Hz, which gives a total conversion time of 200 ms - or sync it to the mains and integrate 16.7 resp. 20 ms), which is often needed for sensor signals.

You can use the other 4051 inputs (or even two or more 4051s) for more input channels, which can be converted sequentially. Slow, but reliable.

Tilmann

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Reply to
Tilmann Reh

There are versions of the TI MSP430 that have 16-bit S-D ADCs.

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Grant Edwards                   grante             Yow! I selected E5 ... but
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Reply to
Grant Edwards

How about the AD7143 @ $1.24 for 1000pcs. 43.5 SPS, 3.3mW, 8 channel, 4mm x

4mm package.

Thomas

Reply to
Thomas Magma

The problem with microcontrollers with on-chip ADC/DACs is that you might not get the nominal 98 dB SNR due to the noise from the controller.

Is DC accuracy (drifts) important in your application ?

Is this ADC part of a control loop, in which case it would be preferable that the ADC is monotonous.

Paul

Reply to
Paul Keinanen

Besides, the high performance ADCs and the microcontrollers are the two different technologies. The MCUs with the good ADC/DACs usually contain two separate dies in one package. For that reason they are more expensive then the equvalent micro + equvalent ADC/DAC.

I am wondering of what could be a sensor which requires the ADC with the true 16-bit accuracy. For the sensor application, that sounds unreasonable to me. Especially considering that the rest of application is handled by a small micro. Apparently there is a problem with the concept.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

ITYM "monotonic"-- did a spell chequer get you? ;-)

Making a slope-type ADC with ~16 bit resolution isn't all that hard, nor is adding some dither and oversampling with a successive- approximation type converter.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Some of the newer microcontrollers such as the MSP430 get around this problem by using very low power operation. Others take their samples while the microcontroller is in sleep mode.

Reply to
Gary Reichlinger

Plenty of sensors are read with 16-bit ADCs. Examples: pressure sensor, strain gauge, position sensors, etc. Just take a look at the Analog Devices app notes.

Reply to
mw

Plenty of them.

I know of quite a few applications that are using 20 and 24 bit ADCs. 16 bits really isn't pushing the limits at all.

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Reply to
Grant Edwards

Anyway, he didn't specify what the accuracy was. 16 bit resolution is pretty unremarkable for control applications.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Yes, but the question is why? That gives a result to 1 part in

65535 over the range, and even if we assign the high order bit to allow overruns by a factor of 2, it is still 1 part in 32767. I find such precision requirements to be extremely rare.
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Reply to
CBFalconer

I'm use to processing photosensor data. Photodiodes can be linear over a huge dynamic range - I was told 14 decades but I've only tried six. I typically want 10-bit accuracy, so some of this can be handled with a gain switch.

I've processed temperature sensor data with 0.001°C resolution (but less accuracy), required for good closed loop performance.

Audio data is another that needs good linearity but can tolerate scale errors.

But I would help if the OP explained what he wanted the ADC for so that we can assess what aspects of the system require 16-bitness.

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Peter
Reply to
Peter Dickerson

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