Download Download, PDF Format(130kB) © Jul 22, 2002, Maxim Integrated Products, Inc. Gain error is usually expressed in LSB or as a percent of full-scale range (%FSR), and it can be calibrated out with hardware or in software. That input frequency is defined as the full-power input bandwidth. Figure 10: FFT showing harmonic distortion (Equation 5) The magnitude of harmonic distortion diminishes at high frequencies to the point that its magnitude is less than the noise floor or is

Aperture Jitter Aperture jitter (tAJ) is the sample-to-sample variation in the aperture delay, as shown in this figure. Everything else is noise--the unwanted signals--to be characterized with respect to the desired signal. If the difference is 1LSB apart, the DNL error is zero. For example, a 12-bit ADC with 4LSBs of integral nonlinearity error can give only 10 bits of accuracy at best (assuming the offset and gain errors have been calibrated).

The signals f1 and f2 are of equal amplitude and very close to one another in frequency. Quantization error is an artifact of representing an analog signal with a digital number (in other words, an artifact of analog-to-digital conversion). Figure 2 shows the full-scale error at the last code transition. Midscale is represented by a one (the MSB) followed by all zeros (10...000).

COMMUNITY Latest Blogs Design Ideas Events Loading... The inverting input of the output amplifier is available for external connection, and the feedback path must be closed externally. ADC 2: The full scale error is equal to the gain error: 0.00 + -0.70 LSB = -0.70 LSB. It is the deviation (of the end point or best fit reference line) from the ideal slope of the transfer characteristic.

We must look to the AC specs to get a good feeling for AC performance. APP 641: Jul 22, 2002 TUTORIAL 641, AN641, AN 641, APP641, Appnote641, Appnote 641 × Login to MyMaxim Email address Password Not registered? Ideally, last transition takes place at Â½ LSB before the rail voltage. SINAD is defined as the RMS value of an input sine wave to the RMS value of the noise of the converter (from DC to the Nyquist frequency, including harmonic [total

Quantization error also affects accuracy, but it's inherent in the analog-to-digital conversion process (and so does not vary from one ADC to another of equal resolution). To prevent aliasing, you must adequately filter all undesired signals so the ADC does not digitize them. Other sources of noise include thermal noise, 1/ƒ noise, and sample clock jitter. This is due to the various offsets of ADC. 1 members found this post helpful. 4th February 2012,08:25 4th February 2012,08:29 #3 soumen21 Member level 3 Join Date May

INL is often called 'relative accuracy.' See also application note INL/DNL Measurements for High-Speed Analog-to-Digital Converters (ADCs). This means that your 12-bit converter can provide only 0.05% accuracy at best. Len Staller serves as an applications engineer for Silicon Laboratories' microcontroller products. The best fitting line calculation uses all transition points.

It is a measure of the straightness of the transfer function. The time now is 01:26. For an ADC, it is essential that the time required for voltage on the sampling capacitor to settle to within 1 LSB be less than the converter's acquisition time. Only harmonics within the Nyquist limit are included in the measurement.

Root Mean Square (RMS) The RMS value of an AC waveform is the effective DC value or DC-equivalent of that signal. ILSB is the ideal LSB step. There is a good reason why manufacturers do not give maximum limits: This increases the cost. Read this Next Managing Noise in the Signal Chain, Part 1: Annoying Semiconductor Noise, Preventable or Inescapable?

For DACs, resolution is similar but reversed--incrementing the code applied to a higher resolution DAC produces smaller step sizes in the analog output. The theoretical best SNR is calculated in Equation 4. Harmonic A harmonic of a periodic signal is a sinewave multiple of the signal's fundamental frequency. Note that the 30µV noise spec equates to 180µV peak-to-peak, which is one-third of an LSB at the 12-bit level and one-sixth of an LSB at the 11-bit level (which is

The maximum deviation from the zero line (the zero line is the reference line) is the INLE. So only the first and last points are used for the calculation of the reference line. Nonlinear errors include integral non-linearity error and differential non-linearity error. Although manufacturers use common terms to describe analog-to-digital converters (ADCs), the way ADC makers specify the performance of ADCs in data sheets can be confusing, especially for a newcomers.

For requests to copy this content, contact us. This gives the engineer more information on how the ADC's performance can be expected to deviate from the numbers posted as typical. See also application note Filter Basics: Anti-Aliasing Aperture Delay Aperture delay (tAD) in an ADC is the interval between the sampling edge of the clock signal (the rising edge of the Oversampling improves the ADC's dynamic performance by effectively reducing its noise floor.

See also application note Demystifying Sigma-Delta ADCs Phase-Matching Phase matching indicates how well matched are the phases of identical signals applied to all channels in a multichannel ADC. Performance specifications can also be a guarantee that an ADC will perform in a certain way. In still other systems, absolute accuracy is not critical, but relative accuracy is. Data sheets typically specify to what order the harmonic distortion has been calculated.

For a DAC, offset error is the analog output response to an input code of all zeros. Two's Complement Coding Two's complement is a digital coding scheme for positive and negative numbers that simplifies addition and subtraction computations. Engineers minimize outside sources of error when assessing the performance of an ADC and in their system design. First apply zero volts to the ADC input and perform a conversion; the conversion result represents the bipolar zero offset error.

An ADC is monotonic if the digital output code always increases as the ADC analog input increases. This guide will help engineers to better understand the specifications commonly posted in manufacturers' data sheets that describe the performance of successive approximation register (SAR) ADCs. Binary Coding (Unipolar) Straight binary is a coding scheme typically used for unipolar signals. Note that the transfer function has pivoted around point A, which moves the zero point away from the desired transfer function.

In such applications, the measured voltage is related to some physical measurement, and the absolute accuracy of the voltage measurement is important. Such distortion is observed as "spurs" in the FFT at harmonics of the measured signal as illustrated in Figure 10. For the ADC, let's assume that the conversion-rate, interface, power-supply, power-dissipation, input-range, and channel-count requirements are acceptable before we begin our evaluation of the overall system performance. In differential systems, where the signal is not referenced to ground but where the positive input is referenced to the negative input, a bipolar signal is one in which the positive

Significant code-edge noise means that an average of samples must be taken to effectively remove this noise from the converter results. If a 2.5V reference has 500µV of peak-to-peak voltage noise at the output (or 83µV RMS), this noise represents 0.02% error or barely 12-bit performance, and this is before any of Common-Mode Rejection (CMR) Common-mode rejection is the ability of a device to reject a signal that is common to both inputs. IMD includes the effects of harmonic distortion and two-tone distortion.

See also application note INL/DNL Measurements for High-Speed Analog-to-Digital Converters (ADCs) Digital Feedthrough Digital feedthrough is the noise that appears on a DAC output when the digital control lines are toggled. For an ideal data converter, the first transition occurs at 0.5LSB above zero.