TZA3000HL Philips Semiconductors, TZA3000HL Datasheet - Page 7

• Manufacturer Part Number: TZA3000HL
• Description: SDH/SONET STM4/OC12 optical receiver
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The TZA3000 contains five functional blocks:
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 A.
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 V
between BWC and AGND.
1997 Oct 17
Preamplifier input stage
Low-pass filter
Limiting amplifier stage
Offset compensation loop
Loss-of-signal detection unit.
SDH/SONET STM4/OC12 optical receiver
ref
(pin 11) or increased by connecting a resistor
7
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 V
into LOSTH. The default value for the external resistor is
86 k . In this case, the current through LOSTH will be
approximately 17.4 A 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 A. 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 s.
CCA
can be used, or a current can be forced
Objective specification
TZA3000