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SY10E446

SY100E446

Micrel, Inc.

M9999-032206

hbwhelp@micrel.com or (408) 955-1690

APPLICATIONS INFORMATION

The SY10E/100E446 are integrated 4:1 parallel-to-serial

converters. The chips are designed to work with the E445

device to provide both transmission and receiving of a high-

speed serial data path.

The E446 can convert 4 bits of

data into a 1.3Gb/s NRZ data stream. The device features

a SYNC input which allows the user to reset the internal

clock circuitry and restart the conversion sequence (see

Timing Diagram A). Note that SOUT is triggered by negative

clock edges.

The E446 features a differential serial input and internal

divide-by-eight circuitry to facilitate the cascading of two

devices to build an 8:1 multiplexer. Figure 1 illustrates the

architecture for an 8:1 multiplexer using two E446s (see

Timing Diagram B). Notice the serial outputs (SOUT) of the

lower order converter feed the serial inputs of the higher

order device. This feed through of the serial inputs bounds

the upper end of the frequency of operation. The clock-to-

serial output propagation delay, plus the set-up time of the

serial input pins, must fit into a single clock period for the

cascade architecture to function properly. Using the worst

case values for these two parameters from the data sheet,

a minimum period of 1400ps or a clock frequency of

700MHz.

The clock frequency is somewhat lower than that of a

single converter. In order to increase this frequency, it is

recommended that the clock edge feeding the E446A be

delayed with respect to the E446B, as shown in Figure 2.

Perhaps the easiest way to delay the second clock relative

to the first is to take advantage of the differential clock

inputs of the E446. By connecting the clock for E446A to

the complimentary clock input pin, the device will clock a

half a clock period after E446B (Figure 2).

Utilizing this

simple technique will raise the potential conversion frequency

up to the maximum 1.3GHz of a stand-alone E446.

Figure 1. Cascaded 8:1 Converter Architecture

E446B

SOUT

SOUT

E446A

SOUT

SOUT

SIN

SIN

CLK

CLK

SERIAL

DATA

PARALLEL DATA

1400ps

200ps

CLK

CLK to SOUT

1600ps