tza3026 NXP Semiconductors, tza3026 Datasheet - Page 7

• Manufacturer Part Number: tza3026
• Description: Tza3026 Sdh/sonet Stm4/oc12 Transimpedance Amplifier
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14763
Product data sheet
7.3 Monitoring RSSI via IDREF_MON
For applications where the transimpedance is controlled by the TIA it is advised to leave
the AGC pads unconnected to achieve fast attack and decay times.
The AGC function can be overruled by applying a voltage to pad AGC. In this
configuration, connecting pad AGC to ground gives maximum transimpedance and
connecting it to V
AGC voltage should be derived from the V
For maximum freedom on bonding location, 2 pads are available for AGC (pads 6 and 15).
These pads are internally connected. Both pads can be used if necessary.
To facilitate RSSI monitoring in modules (e.g. SFF8472 compliant SFP modules), a
current output is provided. This output gives a current which is 20 % of the average DREF
current through the 300
output, a voltage proportional with the average input power can be obtained.
The RSSI monitoring is implemented by measuring the voltage over the 300
resistor. This method is preferred over simple current mirror because at small photo
currents the voltage drop over the resistor is very small. This gives a higher bias voltage
yielding better performance of the photodiode.
For maximum freedom on bonding location, 2 pads are available for IDREF_MON (pads 5
and 16). These pads are internally connected. Both pads can be used if necessary. If only
one is used, the other can be left open.
Fig 7. Transimpedance as function of the AGC voltage
CC
transimpedance
gives minimum transimpedance. This is depicted in
10
(k )
10
10
0.3V
Rev. 01 — 2 May 2005
1
2
1
bias resistor. By connecting a resistor to the IDREF_MON
CC
SDH/SONET STM4/OC12 transimpedance amplifier
0.5V
CC
CC
for proper functioning.
0.7V
CC
V
AGC
001aac623
(V)
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
0.9V
CC
TZA3026
Figure
bias
7. The
7 of 15