ACS411CS datasheet(2/43 Pages) SEMTECH

2 / 43 page

ACS411CS PRE-RELEASE Issue 6.0 July 1999.

PORB

The Power On Reset (PORB) pin resets the device

if forced low for 2ms or more. In normal operation

PORB should be held High. It is recommended that

PORB is connected to VD+ via a 100K

Ω resistor

and to GND via a 100nF capacitor.

System Clock

The system clock on the ACS411CS is derived locally

using the on-chip crystal oscillator and multiplying

PLL.

The oscillator (XTO/I) requires the use of a

fundamental parallel resonance crystal with

appropriate padding capacitors. The crystal

specification should be:

Calibration tolerance: +/- 20ppm @ 25°C

Temp. tolerance:

+/-20ppm @ -40 to +85°C

Temperature range:

-40 to +85°C

Load condition:

parallel load 15pF

Padding capacitor:

18-22pF (tune for desired tolerance)

The system clock defines the burst frequency at

which data is transmitted over the optical link via the

optical interface. The receive circuitry within the

ACS4110 recovers the clock from the received data

at the RXDAT inputs and produces a clock that is

synchronised to the incoming data stream. The

system clock must have a maximum tolerance of +/-

50ppm over the desired temperature range.

Optical Operational Modes

The ACS411CS has four optical operational modes,

all supporting twin fiber.

The ACS9020 can also

utilise Lasers/LED and PIN combinations, including

a PIN with an internal Trans-Impedence Amplifier

(TIA) controlled by PINRX.

The twin fiber Laser modes in Table 1 may be

converted to single fiber operation simply by

interfacing to Wave Division Multiplexer (WDM)

device indicated by mode 5.

Mode

Optical Device

Laser and PIN diode without TIA.

Laser and PIN diode with integrated TIA.

LED and PIN diode without TIA.

LED and PIN diode diode with integrated TIA.

WDM

Table 1: Optical modes

The ACS411CS comprises a chip set of two/three

(link budget dependent) highly integrated devices,

the ACS9020 and ACS4110. The ACS9020 is an

analogue device and the ACS4110 is predominately

a digital device.

The ACS9020 contains the Laser/LED driver as well

as the PIN receiver circuitry. Since the devices are

transmitting and receiving continuously, for long haul

applications two ACS9020 devices are required, one

configured as the transmitter and the other configured

as the receiver.

The ACS4110 comprises the logic necessary to time

compress and decompress the data, plus clock

recovery and all the logic associated with valid data

transmission and reception and locking status. The

ACS4110 also has a configurable parallel

microprocessor bus interface for device configuration

(control) and status analysis. The device setup is

also possible via the far end (remote control) or

directly via pins for the basic device setup.

For the purpose of this specification the chip-set will

be referred to as the ACS411CS and the individual

devices as the ACS9020 or ACS4110.

For low link budget applications (up to 10dB) two

chips, the ACS9020 analogue IC (including laser

driver and PIN receiver circuitry) and the ACS4110

are sufficient.

For applications requiring a higher link budget (up to

30dB) a three chip solution has to be used, where

the laser driver and PIN receiver circuitry are

separated.

Inter-Modem Coding

The inter-IC coding between communication modems

is 8B10B. Whilst transparent to the user, 8B10B

encoding ensures that there is no DC component in

the signal, and provides frequent data transitions,

factors which ease the task of data recovery and

clock extraction.

The coding rules are continuously checked to ensure

the integrity of the link, and errors are indicated on

the ERRL and ERRC pins

(see section headed

ERRC and ERRL - Error Detection ).

Transmit and Receive functions

Data presented at the near-end TPOS/TNEG is time-

compressed, encoded in the 8B10B format and

transmitted over the fiber link to the far end receiver.

Similarly, data presented at the far-end TPOS/TNEG

is time-compressed, encoded in the 8B10B format

and transmitted over the other fiber link to the near

end.

Acapella Optical Modem IC

ACS411CS

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