SLAA694A February   2016  – April 2016 MSP430BT5190 , MSP430BT5190 , MSP430F1122 , MSP430F1122 , MSP430F1132 , MSP430F1132 , MSP430F1222 , MSP430F1222 , MSP430F1232 , MSP430F1232 , MSP430F133 , MSP430F133 , MSP430F135 , MSP430F135 , MSP430F147 , MSP430F147 , MSP430F148 , MSP430F148 , MSP430F149 , MSP430F149 , MSP430F155 , MSP430F155 , MSP430F156 , MSP430F156 , MSP430F157 , MSP430F157 , MSP430F1610 , MSP430F1610 , MSP430F1611 , MSP430F1611 , MSP430F1612 , MSP430F1612 , MSP430F167 , MSP430F167 , MSP430F168 , MSP430F168 , MSP430F169 , MSP430F169 , MSP430F2002 , MSP430F2002 , MSP430F2012 , MSP430F2012 , MSP430F2112 , MSP430F2112 , MSP430F2122 , MSP430F2122 , MSP430F2132 , MSP430F2132 , MSP430F2232 , MSP430F2232 , MSP430F2234 , MSP430F2234 , MSP430F2252 , MSP430F2252 , MSP430F2254 , MSP430F2254 , MSP430F2272 , MSP430F2272 , MSP430F2274 , MSP430F2274 , MSP430F2274-EP , MSP430F2274-EP , MSP430F233 , MSP430F233 , MSP430F235 , MSP430F235 , MSP430F2410 , MSP430F2410 , MSP430F2416 , MSP430F2416 , MSP430F2417 , MSP430F2417 , MSP430F2418 , MSP430F2418 , MSP430F2419 , MSP430F2419 , MSP430F247 , MSP430F247 , MSP430F248 , MSP430F248 , MSP430F249 , MSP430F249 , MSP430F249-EP , MSP430F249-EP , MSP430F2616 , MSP430F2616 , MSP430F2617 , MSP430F2617 , MSP430F2618 , MSP430F2618 , MSP430F2619 , MSP430F2619 , MSP430F2619S-HT , MSP430F2619S-HT , MSP430F4132 , MSP430F4132 , MSP430F4152 , MSP430F4152 , MSP430F435 , MSP430F435 , MSP430F436 , MSP430F436 , MSP430F437 , MSP430F437 , MSP430F438 , MSP430F438 , MSP430F439 , MSP430F439 , MSP430F447 , MSP430F447 , MSP430F448 , MSP430F448 , MSP430F449 , MSP430F449 , MSP430F4616 , MSP430F4616 , MSP430F4617 , MSP430F4617 , MSP430F4618 , MSP430F4618 , MSP430F4619 , MSP430F4619 , MSP430F5132 , MSP430F5132 , MSP430F5152 , MSP430F5152 , MSP430F5172 , MSP430F5172 , MSP430F5222 , MSP430F5222 , MSP430F5224 , MSP430F5224 , MSP430F5229 , MSP430F5229 , MSP430F5242 , MSP430F5242 , MSP430F5244 , MSP430F5244 , MSP430F5247 , MSP430F5247 , MSP430F5249 , MSP430F5249 , MSP430F5253 , MSP430F5253 , MSP430F5255 , MSP430F5255 , MSP430F5257 , MSP430F5257 , MSP430F5259 , MSP430F5259 , MSP430F5304 , MSP430F5304 , MSP430F5308 , MSP430F5308 , MSP430F5309 , MSP430F5309 , MSP430F5310 , MSP430F5310 , MSP430F5324 , MSP430F5324 , MSP430F5325 , MSP430F5325 , MSP430F5326 , MSP430F5326 , MSP430F5327 , MSP430F5327 , MSP430F5328 , MSP430F5328 , MSP430F5328-EP , MSP430F5328-EP , MSP430F5329 , MSP430F5329 , MSP430F5333 , MSP430F5333 , MSP430F5335 , MSP430F5335 , MSP430F5336 , MSP430F5336 , MSP430F5338 , MSP430F5338 , MSP430F5340 , MSP430F5340 , MSP430F5341 , MSP430F5341 , MSP430F5342 , MSP430F5342 , MSP430F5358 , MSP430F5358 , MSP430F5359 , MSP430F5359 , MSP430F5418A , MSP430F5418A , MSP430F5419A , MSP430F5419A , MSP430F5435A , MSP430F5435A , MSP430F5436A , MSP430F5436A , MSP430F5437A , MSP430F5437A , MSP430F5438A , MSP430F5438A , MSP430F5438A-EP , MSP430F5438A-EP , MSP430F5504 , MSP430F5504 , MSP430F5505 , MSP430F5505 , MSP430F5506 , MSP430F5506 , MSP430F5507 , MSP430F5507 , MSP430F5508 , MSP430F5508 , MSP430F5509 , MSP430F5509 , MSP430F5510 , MSP430F5510 , MSP430F5521 , MSP430F5521 , MSP430F5522 , MSP430F5522 , MSP430F5524 , MSP430F5524 , MSP430F5525 , MSP430F5525 , MSP430F5526 , MSP430F5526 , MSP430F5527 , MSP430F5527 , MSP430F5528 , MSP430F5528 , MSP430F5529 , MSP430F5529 , MSP430F5633 , MSP430F5633 , MSP430F5634 , MSP430F5634 , MSP430F5635 , MSP430F5635 , MSP430F5636 , MSP430F5636 , MSP430F5637 , MSP430F5637 , MSP430F5638 , MSP430F5638 , MSP430F5658 , MSP430F5658 , MSP430F5659 , MSP430F5659 , MSP430F6433 , MSP430F6433 , MSP430F6435 , MSP430F6435 , MSP430F6436 , MSP430F6436 , MSP430F6438 , MSP430F6438 , MSP430F6458 , MSP430F6458 , MSP430F6459 , MSP430F6459 , MSP430F6633 , MSP430F6633 , MSP430F6634 , MSP430F6634 , MSP430F6635 , MSP430F6635 , MSP430F6636 , MSP430F6636 , MSP430F6637 , MSP430F6637 , MSP430F6638 , MSP430F6638 , MSP430F6658 , MSP430F6658 , MSP430F6659 , MSP430F6659 , MSP430F67621 , MSP430F67621 , MSP430F67621A , MSP430F67621A , MSP430F67641 , MSP430F67641 , MSP430F6766A , MSP430F6766A , MSP430F6776 , MSP430F6776 , MSP430F6777 , MSP430F6777 , MSP430F6778 , MSP430F6778 , MSP430F6779 , MSP430F6779 , MSP430FG437 , MSP430FG437 , MSP430FG438 , MSP430FG438 , MSP430FG439 , MSP430FG439 , MSP430FG4616 , MSP430FG4616 , MSP430FG4617 , MSP430FG4617 , MSP430FG4618 , MSP430FG4618 , MSP430FG4619 , MSP430FG4619 , MSP430FR2032 , MSP430FR2032 , MSP430FR2033 , MSP430FR2033 , MSP430FR2311 , MSP430FR2311 , MSP430FR2433 , MSP430FR2433 , MSP430FR2532 , MSP430FR2532 , MSP430FR2533 , MSP430FR2533 , MSP430FR2632 , MSP430FR2632 , MSP430FR2633 , MSP430FR2633 , MSP430FR4131 , MSP430FR4131 , MSP430FR4132 , MSP430FR4132 , MSP430FR4133 , MSP430FR4133 , MSP430FR5720 , MSP430FR5720 , MSP430FR5721 , MSP430FR5721 , MSP430FR5724 , MSP430FR5724 , MSP430FR5725 , MSP430FR5725 , MSP430FR5728 , MSP430FR5728 , MSP430FR5729 , MSP430FR5729 , MSP430FR5730 , MSP430FR5730 , MSP430FR5731 , MSP430FR5731 , MSP430FR5734 , MSP430FR5734 , MSP430FR5735 , MSP430FR5735 , MSP430FR5738 , MSP430FR5738 , MSP430FR5739 , MSP430FR5739 , MSP430FR5739-EP , MSP430FR5739-EP , MSP430FR5847 , MSP430FR5847 , MSP430FR58471 , MSP430FR58471 , MSP430FR5848 , MSP430FR5848 , MSP430FR5849 , MSP430FR5849 , MSP430FR5857 , MSP430FR5857 , MSP430FR5858 , MSP430FR5858 , MSP430FR5859 , MSP430FR5859 , MSP430FR5867 , MSP430FR5867 , MSP430FR58671 , MSP430FR58671 , MSP430FR5868 , MSP430FR5868 , MSP430FR5869 , MSP430FR5869 , MSP430FR5870 , MSP430FR5870 , MSP430FR5872 , MSP430FR5872 , MSP430FR58721 , MSP430FR58721 , MSP430FR5887 , MSP430FR5887 , MSP430FR5888 , MSP430FR5888 , MSP430FR5889 , MSP430FR5889 , MSP430FR58891 , MSP430FR58891 , MSP430FR5922 , MSP430FR5922 , MSP430FR59221 , MSP430FR59221 , MSP430FR5947 , MSP430FR5947 , MSP430FR59471 , MSP430FR59471 , MSP430FR5948 , MSP430FR5948 , MSP430FR5949 , MSP430FR5949 , MSP430FR5957 , MSP430FR5957 , MSP430FR5958 , MSP430FR5958 , MSP430FR5959 , MSP430FR5959 , MSP430FR5967 , MSP430FR5967 , MSP430FR5968 , MSP430FR5968 , MSP430FR5969 , MSP430FR5969 , MSP430FR5969-SP , MSP430FR5969-SP , MSP430FR59691 , MSP430FR59691 , MSP430FR5970 , MSP430FR5970 , MSP430FR5972 , MSP430FR5972 , MSP430FR59721 , MSP430FR59721 , MSP430FR5986 , MSP430FR5986 , MSP430FR5987 , MSP430FR5987 , MSP430FR5988 , MSP430FR5988 , MSP430FR5989 , MSP430FR5989 , MSP430FR5989-EP , MSP430FR5989-EP , MSP430FR59891 , MSP430FR59891 , MSP430FR5994 , MSP430FR5994 , MSP430FR6820 , MSP430FR6820 , MSP430FR6822 , MSP430FR6822 , MSP430FR68221 , MSP430FR68221 , MSP430FR6870 , MSP430FR6870 , MSP430FR6872 , MSP430FR6872 , MSP430FR68721 , MSP430FR68721 , MSP430FR6877 , MSP430FR6877 , MSP430FR6879 , MSP430FR6879 , MSP430FR68791 , MSP430FR68791 , MSP430FR6887 , MSP430FR6887 , MSP430FR6888 , MSP430FR6888 , MSP430FR6889 , MSP430FR6889 , MSP430FR6920 , MSP430FR6920 , MSP430FR6922 , MSP430FR6922 , MSP430FR69221 , MSP430FR69221 , MSP430FR6927 , MSP430FR6927 , MSP430FR6928 , MSP430FR6928 , MSP430FR6970 , MSP430FR6970 , MSP430FR6972 , MSP430FR6972 , MSP430FR69721 , MSP430FR69721 , MSP430FR6977 , MSP430FR6977 , MSP430FR6979 , MSP430FR6979 , MSP430FR69791 , MSP430FR69791 , MSP430FR6987 , MSP430FR6987 , MSP430FR6988 , MSP430FR6988 , MSP430FR6989 , MSP430FR6989 , MSP430FR69891 , MSP430FR69891 , MSP430G2131 , MSP430G2131 , MSP430G2132 , MSP430G2132 , MSP430G2152 , MSP430G2152 , MSP430G2153 , MSP430G2153 , MSP430G2230 , MSP430G2230 , MSP430G2230-EP , MSP430G2230-EP , MSP430G2231 , MSP430G2231 , MSP430G2231-EP , MSP430G2231-EP , MSP430G2232 , MSP430G2232 , MSP430G2233 , MSP430G2233 , MSP430G2252 , MSP430G2252 , MSP430G2253 , MSP430G2253 , MSP430G2332 , MSP430G2332 , MSP430G2332-EP , MSP430G2332-EP , MSP430G2333 , MSP430G2333 , MSP430G2352 , MSP430G2352 , MSP430G2353 , MSP430G2353 , MSP430G2432 , MSP430G2432 , MSP430G2433 , MSP430G2433 , MSP430G2444 , MSP430G2444 , MSP430G2452 , MSP430G2452 , MSP430G2453 , MSP430G2453 , MSP430G2513 , MSP430G2513 , MSP430G2533 , MSP430G2533 , MSP430G2544 , MSP430G2544 , MSP430G2553 , MSP430G2553 , MSP430G2744 , MSP430G2744 , MSP430G2755 , MSP430G2755 , MSP430G2855 , MSP430G2855 , MSP430G2955 , MSP430G2955 , MSP430TCH5E , MSP430TCH5E

 

  1.   General Oversampling of MSP ADCs for Higher Resolution
    1.     Trademarks
    2. 1 Introduction
    3. 2 Oversampling Process
      1. 2.1 ADC Operation
      2. 2.2 Improving ADC Resolution
    4. 3 Hardware Description
      1. 3.1 DAC8560EVM
      2. 3.2 MSP-EXP430FR4133 and MSP-EXP432P401R Connections
    5. 4 Firmware Overview
      1. 4.1 Setting Constants
      2. 4.2 Running the Demonstration
      3. 4.3 Oversampling Method Extraction
    6. 5 Results
      1. 5.1 MSP-EXP430FR4133 and DAC8560 Oversampling
      2. 5.2 Silicon Results of Oversampling and Decimation on MSP432P401R
    7. 6 Conclusion
    8. 7 References
  2.   Revision History

2.2 Improving ADC Resolution

Oversampling is a widely popular method for improving ADC resolution. The ADC converts continuous time input signals to a discrete time output. To avoid aliasing and maintain signal fidelity, the ADC sampling rate, FS, needs to be at least twice the maximum frequency information present in the input FIN, also referred to as the Nyquist theorem. Using any sampling rate above this frequency is considered to be oversampling, and its ratio to FSNYQ is called the oversampling ratio (k), shown in Equation 3:

Equation 3. eq3n_k_fs.gif

The effect of oversampling on the noise can be seen clearly in the frequency domain (see Figure 1). When the input is sampled, the entire continuous domain information is translated to and contained within a frequency band of ±FS/2. The total noise power from contributors of white noise, such as thermal and quantization sources, thereby reduces the power spectral density or noise floor in the ADC output's FFT.

fig01n_Noise_Floor_Comparison.gifFigure 1. Noise Floor Comparison of ADCOUT With Sampling Rate of 128 and 1024 kHz

By using a digital filter, it is possible to reduce the quantization noise, and the resulting SNR is improved because the signal at the frequency band of interest is not affected by the filter. For every octave increase in sampling frequency the noise floor can be seen to go down by ~3 dB. Hence if only the noise of the signal band of interest is considered, SNR can be improved as such:

Equation 4. eq4n_snr_osr.gif

FromEquation 3 and Equation 4, the required sampling rate for a desired increase of β in ENOB is:

Equation 5. eq5n_4b_fsynq.gif

Figure 2 shows the signal flow diagram for the oversampling method. Quantization noise is modeled as white noise added to the input signal while sampling, oversampling in turn provides approximately 3 dB (or a half bit of resolution gain) for each doubling of k. The value of k required is therefore determined by taking four to the power of the extra bits of resolution desired.

sig_flow_laa323.gifFigure 2. Signal-Flow Diagram for Oversampling Method

Table 1 describes the relationship between k, SNR, and the achievable extra bits of resolution.

Table 1. Relationship Between Oversampling Factor, SNR, and Extra Bits of Resolution

Oversampling Factor (K) SNR Improvement (dB) Extra Bits of Resolution
2 3 0.5
4 6 1
8 9 1.5
16 12 2
32 16 2.5
64 18 3
128 21 3.5
256 24 4
512 27 4.5
1024 30 5
2048 33 5.5
4096 36 6