Rainbow-electronics MAX1215 Uživatelský manuál stáhnout pdf (Strana 18)

MAX1215

1.8V, 12-Bit, 250Msps ADC for

Broadband Applications

18 ______________________________________________________________________________________

Noise-Power Ratio (NPR)

NPR is commonly used to characterize the return path of

cable systems where the signals are typically individual

quadrature amplitude-modulated (QAM) carriers with a

frequency spectrum similar to noise. Numerous such

carriers are operated in a continuous spectrum, generat-

ing a noise-like signal, which covers a relatively broad

bandwidth. To test the MAX1215 for NPR, a “noise-like”

signal is passed through a high-order bandpass filter to

produce an approximately square spectral pedestal of

noise with about the same bandwidth as the signals

being simulated. Following the bandpass filter, the signal

is passed through a narrow band-reject filter to produce

a deep notch at the center of the noise pedestal. Finally,

this signal is applied to the MAX1215 and its digitized

results analyzed. The RMS noise power of the signal

inside the notch is compared with the RMS noise level

outside the notch using an FFT. Note that the NPR test

requires sufficiently long data records to guarantee a

suitable number of samples inside the notch. NPR for the

MAX1215 was determined for 50MHz noise bandwidth

signals, simulating a typical cable signal environment

(see the Typical Operating Characteristics for test details

and results), and with a notch frequency of 28.8MHz.

Pin-Compatible, Lower-

Speed/Resolution Versions

Applications that require lower resolution and/or higher

speed can refer to other family members of the MAX1215.

Adjusting an application to a lower resolution has been

simplified by maintaining an identical pinout for all mem-

bers of this high-speed family. See the Pin-Compatible

Versions table on the first page of this data sheet for a

selection of different resolution and speed grades.

Pin Configuration

5859606162 5455565763

AGND

TOP VIEW

OGND

ORP

ORN

D11P

D11N

D10P

D10N

5253

D9P

D9N

AGND

CLKN

CLKP

AGND

OGND

D0N

D1N

D0P

D1P

D6P

D6N

OGND

DCLKP

DCLKN

D5P

D5N

D4P

37 D4N

D3P

D3N

AGND

INN

INP

AGND

REFADJ

REFIO

AGND

48 D7N

AGND

656667

AGND

T/B

2322212019 2726252418 2928 323130

D2N

D2P

3433

D8N

D7P

51 D8P

CLKDIV 17

MAX1215

QFN

1 2 ... 13 14 15 16 17 18 19 20

Broadband Applications 1

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