MAX1448 查看數據表（PDF） - Maxim Integrated

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MAX1448

10-Bit, 80Msps, Single 3.0V, Low-Power ADC with Internal Reference

Maxim Integrated 

10-Bit, 80Msps, Single 3.0V, Low-Power

ADC with Internal Reference

Grounding, Bypassing,

and Board Layout

The MAX1448 requires high-speed board layout design

techniques. Locate all bypass capacitors as close to

the device as possible, preferably on the same side as

the ADC, using surface-mount devices for minimum

inductance. Bypass VDD, REFP, REFN, and COM with

two parallel 0.1µF ceramic capacitors and a 2.2µF

bipolar capacitor to GND. Follow the same rules to

bypass the digital supply (OVDD) to OGND. Multilayer

boards with separated ground and power planes pro-

duce the highest level of signal integrity. Consider

using a split ground plane arranged to match the physi-

cal location of the analog ground (GND) and the digital

output driver ground (OGND) on the ADC's package.

The two ground planes should be joined at a single

point so that the noisy digital ground currents do not

interfere with the analog ground plane. The ideal loca-

tion of this connection can be determined experimen-

tally at a point along the gap between the two ground

planes that produces optimum results. Make this con-

nection with a low-value, surface-mount resistor (1Ω to

5Ω), a ferrite bead, or a direct short. Alternatively, all

ground pins could share the same ground plane if the

ground plane is sufficiently isolated from any noisy, dig-

ital systems ground plane (e.g., downstream output

buffer or DSP ground plane). Route high-speed digital

signal traces away from sensitive analog traces. Keep

all signal lines short and free of 90° turns.

Static Parameter Definitions

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values

on an actual transfer function from a straight line. This

straight line can be either a best straight-line fit or a line

drawn between the endpoints of the transfer function

once offset and gain errors have been nullified. The

MAX1448’s static linearity parameters are measured

using the best straight-line fit method.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between

an actual step width and the ideal value of 1LSB. A

DNL error specification of less than 1LSB guarantees

no missing codes and a monotonic transfer function.

Dynamic Parameter Definitions

Aperture Jitter

Figure 12 depicts the aperture jitter (tAJ), which is the

sample-to-sample variation in the aperture delay.

Aperture Delay

Aperture delay (tAD) is the time defined between the

falling edge of the sampling clock and the instant when

an actual sample is taken (Figure 12).

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 A/D noise is caused by quantization error only

and results directly from the ADC’s resolution (N bits):

SNR(MAX) = (6.02 x N + 1.76)dB

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, which includes all spectral

components minus the fundamental, the first five har-

monics, and the DC offset.

Signal-to-Noise Plus Distortion (SINAD)

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

nal to all spectral components minus the fundamental

and the DC offset.

Effective Number of Bits (ENOB)

ENOB specifies the dynamic performance of an ADC at

a specific input frequency and sampling rate. An ideal

ADC’s error consists of quantization noise only. ENOB

is computed from:

ENOB = (SINAD − 1.76)

6.02

Total Harmonic Distortion (THD)

THD is typically the ratio of the RMS sum of the input

signal’s first five harmonics to the fundamental itself.

This is expressed as:



THD = 20 × log 

(V22 + V32 + V42 + V52 )

V1



where V1 is the fundamental amplitude, and V2 through

V5 are the amplitudes of the 2nd- through 5th-order

harmonics.

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