ACS102A 查看數據表（PDF） - Semtech Corporation

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ACS102A

Fiber Modem

Semtech Corporation 

Advanced Communications

ACS102A Data Sheet

Mode 7 - Single Fiber 3-pin LASER/PIN mode (Laser recv)

LASER current control

Setup : DP5=0, DP4=0, DP3=0, DP2=0, DP1=0

The LASER output current must be set for each individual device

This is a single-fiber mode where the LASER is used for transmis-

sion and only the LASER is used for reception. Connections are as

in mode 4.

in accordance with the manufacturer’s recommendations. The

output current to the LASER is controlled by a variable resistor

(Rtrc) between TRC and ground. The lower the value of Rtrc the

greater the current. The minimum value of Rtrc is 800Ω. The

ACS102A derives and controls the average optical power being

Preamp Interface modes

produced by measuring the current in the LASER's monitor PIN

Mode 8 - Preamp Voltage Input & LED Drive

diode and integrating this measurement using the capacitor on the

CTX pin, which is typically 10nF. A control loop is established

Setup : DP5=1, DP4=0, DP3=1, DP2=0, DP1=0, NSB=0

This is a mode for use with external amplifier and PIN modules. An

LED is used for transmission and connected as normal with its

anode to LAP and cathode to LAN. The differential voltage from an

external PIN/TIA module is connected to PINN and PINP via

100pF capacitors to provide DC isolation. The signals should be

which works to maintain the average optical power at a constant

level whilst parameters such as voltage, temperature and LASER

efficiencies may vary. The average optical power is always one

half of the peak power since the LASER is driven between full on

and full off, with an average mark-space ratio of 50%. An example

circuit arrangement is shown in figure 6.

connected such that PINP is connected to the TIA output that goes

Adjustment Procedure

high when light is received. A single input can also be applied from

a single ended PIN/TIA by feeding the input to PINP only, PINN is

left floating. This mode uses the new NSB pin, in all other modes

this pin should be left disconnected or connected to VA+.

Select the appropriate LASER drive mode using the pins DP1-5

(see section headed Operational Modes). The LASER drive

current and hence transmitted optical power is set by adjusting

Rtrc until the required output power is obtained, taking account of

Mode 9 - Preamp Voltage Input & LASER Drive

the maximum allowed drive current set by the LASER manufac-

Setup : DP5=1, DP4=0, DP3=1, DP2=0, DP1=1, NSB=0

turer.

This is a mode for use with external amplifier and PIN modules. A

There are two ways of measuring the output power and drive

current, either dynamically in the normal operating mode or

2

LASER is used for transmission and connected as normal as

statically by setting the pin SETB low.

described under mode 3. The differential voltage from an external

PIN/TIA module is connected to PINN and PINP via 100pF

If measuring power dynamically during the normal mode, the

capacitors to provide DC isolation. The signals should be

output from the laser can be measured using an optical-power

connected such that PINP is connected to the TIA output that goes

meter that is capable of detecting peak optical-power. If an

high when light is received. A single input can also be applied from

averaging optical power meter is employed then a correction factor

a single ended PIN/TIA by feeding the input to PINP only. With a

of 16 must be used to obtain the peak value :

LASER drive the PINN and PINP inputs are also connected to the

LASER monitor diode. This may induce extra noise but should not

LASER(peak power) = Laser(average power) * 16.

interfere with the operation. This mode uses the new NSB pin, in

all other modes this pin should be left disconnected or connected

to VA+.

To measure power statically, the SETB pin must be pulled low to

ground. This forces the device to constantly transmit through the

LASER at a fixed level. This fixed level will be equivalent to half of

the peak level, since the normal control loop within the device

Digital interface modes

works to control the average power level through integrating out

the alternating data pulses.

Mode 10 - Digital Data Input & LASER Drive

LASER(peak power) = Laser power(with SETB=0) * 2.

Setup : DP5=0, DP4=1, DP3=1, DP2=0, DP1=0

Since all currents are static in this mode, a simple optical power

This is a mode for use with external amplifier and PIN modules that

meter can be used and the drive current in the laser can be easily

provide fully digital output levels. A LASER is used for transmission

measured by connecting an ammeter between pin LMN and VA+.

and connected as normal as described under mode 3. The output

LMN provides a convenient means of monitoring the LASER drive

from an external PIN/TIA module is connected to CNT. The

current through the relationship :

polarity of the input should be such that CNT that goes high when

light is received.

LASER(current) = 100 x LMN(current) +/- 8%.

Mode 11 - Digital Data Input & LED Drive

Dynamic measurement of the LMN current is also possible by

connecting a resistor to LMN and measuring the voltage pulses.

Setup : DP5=1, DP4=1, DP3=0, DP2=1, DP1=0

This is a mode for use with external amplifier and PIN modules that

provide fully digital output levels. An LED is used for transmission

and connected as normal as shown in figure 5. The output from an

external PIN/TIA module is connected to CNT. The polarity of the

input should be such that CNT that goes high when light is

received.

Transmit Current Control

LED current control

The LED transmit current is not critical though it is important not to

exceed the LED manufacturer's recommendation for maximum

current. The current is controlled by a resistance Rtrc connected

between TRC and GND. The lower the value of Rtrc the greater

the current. The lower limit for Rtrc is 800Ω while a practical

maximum is 40kΩ.

The LED current is inversely proportional to Rtrc while Rtrc > 800Ω.

LED current = (100 / Rtrc) +/- 25 %

Data-Rate Selection

The ACS102A benefits from data compression circuitry which

reduces power consumption and improves the BER (Bit Error

Rate). The compression technique employed, demands a

minimum TxD data-bit time of 10 sample-clocks. This defines the

maximum data rate:

Maximum data rate = sample-clock/10

However, an allowance must be made for any variation in the TxD

data-bit period to accommodate frequency variation and jitter.

Hence the maximum data rates specified in the following are

decreased by 10% to include a sufficient safety margin.

The ACS102A includes an input pulse shaper which ensures that

the system is very tolerant to jitter, and helps achieve a maximum

data-rate close to the theoretical maximum of sample-clock/10

(bps). The pulse shaper will expand data pulses of less than 10

clock-samples to meet the compression criteria. This is performed

on up to three consecutive data-bits which fail to meet the

minimum pulse width criteria.

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