Stand-Alone, 10-Channel, 10-Bit System Monitors

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Gain Error

The gain error is the difference between the ideal and

actual value of the analog input difference between the

first and last transitions of the ADC output. The first

transition is from digital code 0 to code 1, and the last

ADC bits for straight binary output code. For the

MAX1153/MAX1154, the ideal difference in the input

voltage between code transitions 0 to 1 and code tran-

sitions 1022 to 1023 is 1022 x LSB. For the MAX1153,

this is 2.5V - 2 x LSB = 2.495117, and for the MAX1154,

this is 4.096V - 2 x LSB = 4.088. Gain error is a DC

specification, usually normalized to the FS ideal analog

value and given in percent of FSR or ppm.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital

samples, signal-to-noise ratio (SNR) is the ratio of the

full-scale analog input (RMS value) to the RMS quantiza-

tion error (residual error). The ideal theoretical minimum

analog-to-digital noise is caused by quantization error

only, results directly from the ADC’s resolution (N bits),

and can be calculated with the following equation:

SNR = (6.02 x N + 1.76)dB

There are other noise sources besides quantization

noise, including thermal noise, reference noise, clock

jitter, etc. Therefore, SNR is calculated by taking the

ratio of the RMS signal to the RMS noise, which

includes all spectral components minus the fundamen-

tal, the first five harmonics, and the DC offset.

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the

fundamental input frequency’s RMS amplitude to the

RMS equivalent of all other ADC output signals:

There are other noise sources besides quantization

noise, including thermal noise, reference noise, clock

jitter, etc. Therefore, SINAD is calculated by taking the

ratio of the full-scale signal to the RMS noise, which

includes all spectral components minus the fundamen-

tal and the first five harmonics.

Total Harmonic Distortion (THD)

Total harmonic distortion (THD) is the ratio of the RMS

sum of the first five harmonics of the input signal to the

fundamental itself. This is expressed as:

order harmonics, respectively.

Power-Supply Rejection

Power-supply rejection is the ratio between the change

in the ADC full-scale output to the change in power-

supply voltage when the power-supply voltage is varied

from its nominal value. It is specified in V/V or µV/V.

THD

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