AD Converter 12 Bit Integration 20ms

Hi Karl,

For your description it sounds that you are looking for a delta-sigma converter.  One possible option would be the combination of the PGA280+ADS1259.  The ADS1259 is a 24 bit converter that offers sampling rates from 10SPS to 14KSPS (including 50Hz) with SPI compatible interface.  The PGA 280 can work up to +/-10V differential signals as long as the inputs are in the valid voltage range (VSN+2.5 < Range < VSP-2.5) and offers selectable gains from 1/8 to 128. 

 If you would like to integrate the signal on the processor; there may be other options using SAR converters.  What is the application?   Do you need a delta-sigma converter or a SAR converter?

Thank you and Regards,

Luis

Hi Luis,

thanks for your answer.

I won't like to integrate the signal on the processor. How good integrate a sigma delta ADC an anlogsignal?  

I need multiplexer to switch the analog channels and ervery channel will be integrated for 20ms.

Do you have an application note for the signal path with the PGA280+ADS1259?

Hi Karl,

The PGA280 is a high precision instrumentation programmable gain amplifier that may take an input voltage signal and scale the signal optimally for analog to digital conversion.  The ADS1259 is a 24 bit delta sigma converter. In a delta-sigma converter ADC the input signal is oversampled by a modulator, and then filtered and decimated by a digital filter.  This will yield a high resolution data output at a lower sampling rate; the data output code of the converter is an average of the signal over that period of time.  I suggested this device mainly due to your +/-10V differential input signal requirement.

What kind of signal are you trying to integrate?  What kind of sensor are you trying to measure or what is the application?   For example, there are other devices (for example DDC112) is a current input ADC which combines current to voltage conversion, continuous integration, mainly used for low-level current output devices, for example photo sensors.

Thank you,

Luis

The ADS1259 datasheet  shows a complete schematic of a PGA280+ADS1259 application (figure 64, page 41) .  In addition, you may also check the ADS1259EVM evaluation board that includes both the ADS1259 and PGA280 combined together.

Hi Luis,

I'm back on tjis problem:

the ADS1259 is a good selction but it is expensive. Do you have an other proposal with 16Bit with sigma delta, but cheaper then the ADS1259?

Thank you for your help

Hi Karl,

Sorry for the delay.  The PGA280+ADS1259 are designed/optimized to work together...

I need to ask you a few questions to make sure I understand your application:

From the previous postings,  you mentioned a required accuracy >=12bits, SPI interface required and a input range of +/-10V (differential). 

What are the requirements in terms of sampling rate? Does it need to be a delta-sigma converter or would you also consider a SAR converter?

What kind of sensor or what kind of application/measurement are you trying to perform?

Thank you and Regards,

Luis 

Hi Luis,

the analog signal is a DC for example with -6 V to GND with an Overlay ac signal with 0.5V and 50Hz. The sampling rate should be min 25 SPS. The accuracy should be min 12 Bit + sign. If it is able, I don't wont make a software integration.

Thank you and best regards

Karl 

Hi Karl,

I spoke briefly with Luis and we discussed some design possibilities for you. One thing that is going to determine the design and components we choose is price point? The PGA280+ADS1259 sounds like it would fit the application very well as it is geared towards DC applications and slower AC applications with high precision. This 24 bit solution is somewhere are $8.50 as long as you already have an external reference component. If you are looking for lower resolution to reduce the price, there are a few delta sigmas we can offer such as the ADS1146, ADS1147 and ADS1118. Keep in mind that you will need to set the Vocm pin on the PGA280 to make sure that input to the ADC is within limits. The ADS1147 with the PGA280 would allow you to use the internal reference from the ADS1147 to feed the PGA280 Vocm to set the common mode point. Additionally, it includes an internal reference eliminating an additional component from your system. It should be a little cheaper than using the ADS1259 but you do lose 8 bits of resolution.

Regards,

Tony Calabria