GL600USB datasheet(21/38 Pages) ETC

21 / 38 page

06/19/2000

GL600USB/GL600USB-A/GL600USB-B

Revision 1.3

The data receivers for all types of devices must be able to properly decode the differential data in the

presence of jitter. The more of the bit time that any data edge can occupy and still be decoded, the more

reliable the data transfer will be. Data receivers are required to decode differential data transitions that

occur in a window plus and minus a nominal quarter bit time from the nominal (centered) data edge

position. Jitter will be caused by the delay mismatches and by mismatches in the source and destination

data rates (frequencies).

Differential

Data Lines

Paired

Transitions

N * TPERIOD + TJR2

TPERIOD

Consecutive

Transitions

N * TPERIOD + TJR1

TJR

TJR1

TJR2

Figure 4-4 Receiver Jitter Tolerance

The source of data can have some variation (jitter) in the timing of edges of the data transmitted. The time

between any set of data transitions is N*TPeriod ± jitter time, where N is the number of bits between the

transitions and TPeriod is defined as the actual period of the data rate. The data jitter is measured with the

same capacitive load used for maximum rise and fall times and is measured at the crossover points of the

data lines.

For low-speed transmissions, the jitter time for any consecutive differential data transitions must be within

±25ns and within ±10ns for any set of paired differential data transitions. These jitter numbers include

timing variations due to differential buffer delay, rise/fall time mismatches, internal clock source jitter,

noise and other random effects.

The output rise time and fall time are measured between 10% and 90% of the signal. Edge transition time

for the rising and falling edges of low-speed signals is 75ns (minimum) into a capacitive load (CL) of 50pF

and 300ns (maximum) into a capacitive load of 350pF. The rising and falling edges should be transitioning

(monotonic) smoothly when driving the cable to avoid excessive EMI.

Low Speed: 75ns at CL = 50pF, 300ns at CL = 350pF

Full Speed: 4 to 20ns at CL = 50pF

Differential

Data Lines

10%

Rise Time

90%

Fall Time

10%

90%

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