CS61318 datasheet(16/28 Pages) CIRRUS

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CS61318

DS441PP2

pled to their respective grounds. TV+ must not

exceed RV+ by more than 0.3 V.

Decoupling and filtering of the power supplies is

crucial for the proper operation of the analog cir-

cuits in both the transmit and receive paths. A 47

µF

tantalum and 1.0

µF mylar or ceramic capacitor

should be connected between TV+ and TGND, and

a 0.1

µF mylar or ceramic capacitor should be con-

nected between RV+ and RGND. Place capacitors

as closely as possible to their respective power sup-

ply pins. Wire-wrap breadboarding of the line in-

terface is not recommended because lead resistance

and inductance serve to defeat the function of the

decoupling capacitors.

3 ARBITRARY WAVEFORM

GENERATION

In addition to the predefined pulse shapes, the user

can create custom pulse shapes under the Host

Mode operation. This flexibility allows the board

designer to accommodate non-standard cables,

EMI filters, protection circuitry, etc.

The arbitrary pulse shape of mark (a transmitted

“1”) is specified by describing it's pulse shape

across three Unit Intervals (UIs). This allows, for

example, the long-haul return-to-zero tail to extend

into the next UI, or two UIs, as is required for iso-

lated pulses.

Each UI is divided into multiple phases, and the us-

ers defines the amplitude of each phase. The wave-

form of a space (a transmitted “0”) is fixed at zero

volts. Examples of the phases are shown in

Figure 10. In all cases, to define an arbitrary wave-

form, the user writes to the Waveform Register ei-

ther 36, 39 or 42 times (12, 13 or 14 phases per UI

for three UIs). The phases are written in the order:

UI1/phase1,

UI1/phase2,

...

UI1/phase14,

UI2/phase1, ... , UI2/phase14, UI3/phase1, ... ,

UI3/phase14.

The CS61318 divides the 488 ns UI into 14 uni-

form phases (34.9 ns each), and uses the phase in-

formation written for all 14 phases of each UI.

When transmitting pulses, the CS61318 will add

the amplitude information from the prior two sym-

bols with the amplitude of the first UI of the current

symbol before outputting a signal on TTIP/TRING.

Therefore, a mark preceded by two spaces will be

output exactly as the mark is programmed. Howev-

er, when one mark is preceded by marks, the first

portion of the last mark may be modified. With

AMI data, where successive pulses have opposite

polarity, the undershoot tail of one pulse will cause

the rising edge of the next mark to rise more quick-

ly, as shown in Figure 11.

E1 Arbitrary Waveform Example

Figure 10. Phase Definition of Arbitrary Waveform

Figure 11. Example of Summing of Waveforms

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