AD9546SLASHPCBZ datasheet(73/205 Pages) AD

73 / 205 page

Data Sheet

AD9546

Rev. 0 | Page 73 of 205

EMBEDDED

CLOCK

DEMODULATOR

REFB

REFBB

DIFFERENTIAL

SINGLE- ENDED

TIME

STAMPS

TDC

SYNC

Mx PIN

FUNCTION

LOGIC

1-OF-6 LOOPBACK

PATH SELECTOR

SYNC

REG 0x2D02, BITS[2:0]

SINGLE- ENDED

EMBEDDED

CLOCK

DEMODULATOR

÷R

TIME

STAMPS

NOTES

1. A RANGE OF BITS USES A COLON SEPARATOR

REG 0x0106, BIT 7 = 1

Figure 56. Analog Loopback Detail

The TC1 and TC2 time codes occur sequentially in pairs: TC1[x]

and TC2[x], TC1[x + 1] and TC2[x + 1], and so on. Each time

code pair provides a round trip delay measurement, RTD, given by

RTD[x] = TC2[x] − TC1[x]

Ideally, each RTD[x] is the same value, but in practice, the

RTD[x] values vary slightly due to various noise contributors.

Generally, the user takes an average of several RTD[x] values to

yield an improved estimate of round trip delay. The round trip

delay measurement includes all delays in the loopback path:

interconnections and active elements (like buffers and other

semiconductor components). However, Table 29 provides static

delay values for sections of the internal loopback paths, which

the user can subtract from the round trip delay measurement to

account for the delay associated with the internal paths of the

device. The resulting value, RTDCORR, constitutes the corrected

round trip delay, which consists of the total interconnect delay

(forward and reverse paths) along with delay contributions of

any other components in the path. The small error due to the

difference between the mean specified component delays and

the actual component delays also exists. Assuming the

interconnect delay dominates, an approximation of the forward

(or reverse) path interconnect delay, Δt, is

Δt = ½ × RTDCORR

With a value for RTDCORR and knowledge of the mean

component delays in the signal path, the user can program

corrective offsets in the appropriate nodes to counteract the

path delay.

EXCESSIVE ROUND TRIP DELAY

In some applications, interconnect lengths may result in a

round trip delay that exceeds the period of the underlying clock

period. Such a situation breaks the symmetry of the TC1 and

TC2 time code pairs. Techniques exist to overcome excessive

round trip delay, but such is beyond the scope of this data sheet.

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