TZA3000HL データシートの表示（PDF） - Philips Electronics

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TZA3000HL

SDH/SONET STM4/OC12 optical receiver

Philips Electronics 

Philips Semiconductors

SDH/SONET STM4/OC12 optical receiver

Objective specification

TZA3000

FUNCTIONAL DESCRIPTION

The TZA3000 contains five functional blocks:

• Preamplifier input stage

• Low-pass filter

• Limiting amplifier stage

• Offset compensation loop

• Loss-of-signal detection unit.

Preamplifier

The preamplifier provides low-noise amplification of the

current generated by a photodiode connected to the

IPhoto pin.

A differential amplifier converts the output of the

preamplifier to a differential voltage. An AGC loop

increases the dynamic range of the receiver by reducing

the feedback resistance of the preamplifier. The AGC loop

hold capacitor is integrated on-chip, so an external

capacitor is not needed for AGC. The AGC voltage can be

monitored at pin 31. This pin can be left unconnected for

normal operation. It can also be used to force an external

AGC voltage. If pin 31 (AGC) is connected to AGND, the

internal AGC loop is disabled and the receiver gain is at a

maximum. In this case, the maximum input current is about

50 µA.

Low-pass filter

A low-pass filter controls the bandwidth of the receiver,

which can be varied between 300 and 600 MHz.

The bandwidth is set to 470 MHz by default. It can be

decreased by connecting a resistor between BWC (pin 10)

and Vref (pin 11) or increased by connecting a resistor

between BWC and AGND.

Limiting amplifier

A limiting amplifier boosts the signal up to PECL levels.

The output can be either CML or PECL compatible,

selected by means of pin OUTSEL. When OUTSEL is

HIGH, CML data outputs are active and PECL data

outputs are disabled. If OUTSEL is left unconnected, it is

pulled LOW and PECL data outputs are active while CML

data outputs are disabled.

Offset cancellation loop

A control loop connected between the limiting amplifier

output and the differential amplifier input cancels the DC

offset. The loop bandwidth is fixed internally at 30 kHz.

Loss-of-signal detection (LOS)

The LOS section detects an input signal level below a fixed

threshold. The threshold is determined by the current

through pin LOSTH. If this current is increased, the

threshold level will rise. An external resistor between

LOSTH and VCCA can be used, or a current can be forced

into LOSTH. The default value for the external resistor is

86 kΩ. In this case, the current through LOSTH will be

approximately 17.4 µA since the voltage at pin LOSTH is

regulated at 1.5 V below the supply voltage. This threshold

corresponds to an input current of 0.96 µA. The ratio of

LOSTH current to input current is thus approximately

18 : 1. When the input signal level falls below this

threshold, the LOS (PECL compatible) and LOSTTL (TTL

compatible) outputs go HIGH. The hysteresis is fixed

internally at 3 dB. Response time is typically less than

20 µs.

1997 Oct 17

7

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