AD9545BCPZ datasheet(60/157 Pages) AD

60 / 157 page

AD9545

Data Sheet

Rev. A | Page 60 of 157

Each Q divider has a dedicated pair of generators: one for

generating randomized clock signals (PRBS) and another for

supporting burst or gapped clock applications (N-shot), as

shown by the expanded detail of N-shot/PRBS Generator AP in

Figure 48. The enable Qxy PRBS and enable Qxy N-shot bits

select the N-shot/PRBS output clock function (where x is 0 or 1

and y is A, AA, B, BB, C, or CC).

The enable Qxy PRBS bits reside in Register 0x10D4 (Bit 1,

Bit 3, Bit 5, and Bit 7), Register 0x10D5 (Bit 1 and Bit 3), and

The enable Qxy N-shot bits reside in Register 0x10D4 (Bit 0,

Bit 2, Bit 4, and Bit 6), Register 0x10D5 (Bit 0 and Bit 2), and

Table 36 shows a list of the N-shot/PRBS output clock function

selections.

Table 36. N-Shot/PRBS Output Clock Function Selections

Enable Qxy

PRBS

Enable Qxy

N-Shot

Output Clock Function

Normal clock (Q divider)

Burst/gapped clock

Randomized clock

Not applicable

Although it is physically possible to set both enable Qxy PRBS

and enable Qxy N-shot bits to Logic 1, the user must avoid

doing so. This setting is an undefined mode and may result in

unspecified device behavior.

RANDOMIZED CLOCK (PRBS)

When the randomized clock function is in effect, the output

clock signal is a pseudorandom sequence of high and low

output levels generated at the rate of the associated Q divider. A

representation of the output clock signal appears in Figure 49.

The spectrum of a normal clock signal (square wave) is a series

of line spectra consisting of the fundamental clock frequency

and its associated harmonics. The main purpose of a PRBS

clock (or spread spectrum clock) is to broaden the spectral line

of the fundamental in exchange for suppressing the harmonic

spectral lines.

Because the user can program more than one output of the

AD9545 as a spread spectrum clock, each of the 10 PRBS

generators produces a unique PRBS sequence, which prevents

the possibility of correlated crosstalk between outputs enabled

for PRBS clock generation. All 10 PRBS generators have 17th-

order generator polynomials, which means the PRBS sequence

is inherently periodic over a period of 217 − 1 (131,071) Q divider

output cycles.

N-SHOT (JESD204B AND GAPPED CLOCKING)

N-Shot Overview

The ability of the AD9545 to generate JESD204B clock signals

and gapped clock signals derives from it N-shot generators.

Each N-shot generator operates at the rate of the Q divider

output. The user has control over whether the N-shot generator

produces a periodic output clock pattern or single burst pattern.

In either case, triggering a pattern is via the N-shot request

Channel x bit (where x is 0 or 1) in Register 0x2101, Bit 0, and

serve as the N-shot trigger via the Mx pins.

In Figure 48, the N-shot parameters apply to all N-shot

generators in a PLL channel, except for the enable Qxy N-shot

bits, which apply to each individual N-shot generator. As such,

the N-shot parameters are common to all outputs in a channel

that have burst/gapped clock functionality enabled (per Table 36).

Using the N-shot generators imposes a minimum divide ratio of

8 on the associated Q dividers.

Q DIVIDER

OUTPUT

PRBS

SEQUENCE

CLOCK

OUTPUT

Q DIVIDER PERIOD BASED ON ITS INPUT CLOCK AND DIVIDE RATIO

TIME

Figure 49. PRBS Clock Signal

AD9545BCPZ датащи(PDF) 60 Page - Analog Devices

AD9545BCPZ датащи(HTML) 60 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL