MAX12528 datasheet(25/28 Pages) MAXIM

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mount devices for minimum inductance. Bypass VDD to

GND with a 220µF ceramic capacitor in parallel with at

least one 10µF, one 4.7µF, and one 0.1µF ceramic

capacitor. Bypass OVDD to GND with a 220µF ceramic

capacitor in parallel with at least one 10µF, one 4.7µF,

and one 0.1µF ceramic capacitor. High-frequency

bypassing/decoupling capacitors should be located as

close as possible to the converter supply pins.

Multilayer boards with ample ground and power planes

produce the highest level of signal integrity. All grounds

and the exposed backside paddle of the MAX12528

package (package code: T6800-2) must be connected

to the same ground plane. The MAX12528 relies on the

exposed backside paddle connection for a low-induc-

tance ground connection. Isolate the ground plane

from any noisy digital system ground planes such as a

DSP or output buffer ground.

Route high-speed digital signal traces away from the

sensitive analog traces. Keep all signal lines short and

free of 90

° turns.

Ensure that the differential, analog input network layout

is symmetric and that all parasitic components are bal-

anced equally. Refer to the MAX12528 EV kit data

sheet for an example of symmetric input layout.

Parameter Definitions

Integral Nonlinearity (INL)

INL is the deviation of the values on an actual transfer

function from a straight line. For the MAX12528, this

straight line is between the endpoints of the transfer

function, once offset and gain errors have been nulli-

fied. INL deviations are measured at every step of the

transfer function and the worst-case deviation is report-

ed in the Electrical Characteristics table.

Differential Nonlinearity (DNL)

DNL is the difference between an actual step width and

the ideal value of 1 LSB. A DNL error specification of

less than 1 LSB guarantees no missing codes and a

monotonic transfer function. For the MAX12528, DNL

deviations are measured at every step of the transfer

function and the worst-case deviation is reported in the

Electrical Characteristics table.

Offset Error

Offset error is a figure of merit that indicates how well

the actual transfer function matches the ideal transfer

function at a single point. Ideally, the midscale

MAX12528 transition occurs at 0.5 LSB above mid-

scale. The offset error is the amount of deviation

between the measured midscale transition point and

the ideal midscale transition point.

Gain Error

Gain error is a figure of merit that indicates how well the

slope of the actual transfer function matches the slope of

the ideal transfer function. The slope of the actual trans-

fer function is measured between two data points: posi-

tive full scale and negative full scale. Ideally, the positive

full-scale MAX12528 transition occurs at 1.5 LSBs below

positive full scale, and the negative full-scale transition

occurs at 0.5 LSB above negative full scale. The gain

error is the difference of the measured transition points

minus the difference of the ideal transition points.

Small-Signal Noise Floor (SSNF)

SSNF is the integrated noise and distortion power in the

Nyquist band for small-signal inputs. The DC offset is

excluded from this noise calculation. For this converter,

a small signal is defined as a single tone with an ampli-

tude of -35dBFS. This parameter captures the thermal

and quantization noise characteristics of the data con-

verter and can be used to help calculate the overall

noise figure of a digital receiver signal path.

Signal-to-Noise Ratio (SNR)

For a waveform perfectly reconstructed from digital

samples, the theoretical maximum SNR is the ratio of

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

quantization error (residual error). The ideal, theoretical

minimum analog-to-digital noise is caused by quantiza-

tion error only and results directly from the ADC’s reso-

lution (N bits):

SNR[max] = 6.02

× N + 1.76

In reality, there are other noise sources besides quanti-

zation noise: thermal noise, reference noise, clock jitter,

etc. SNR is computed by taking the ratio of the RMS

signal to the RMS noise. RMS noise includes all spec-

tral components to the Nyquist frequency excluding the

fundamental, the first six harmonics (HD2 through

HD7), and the DC offset.

SNR = 20 x log (SIGNALRMS / NOISERMS)

Signal-to-Noise Plus Distortion (SINAD)

SINAD is computed by taking the ratio of the RMS sig-

nal to the RMS noise plus distortion. RMS noise plus

distortion includes all spectral components to the

Nyquist frequency excluding the fundamental and the

DC offset.

Dual, 80Msps, 12-Bit, IF/Baseband ADC

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