tza3026 NXP Semiconductors, tza3026 Datasheet - Page 5

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

Philips Semiconductors
9397 750 14763
Product data sheet
The parasitic capacitance can be minimized through:
The PIN diode can be biased with a positive or a negative voltage.
diode biased positively, using the on-chip bias pad DREF. The voltage at DREF is derived
from V
which decouples any supply voltage noise. The value of external capacitor C2 affects the
value of PSRR and should have a minimum value of 470 pF. Increasing this value
improves the value of PSRR. The current through R
IDREF_MON, see
If the biasing for the PIN diode is done external to the IC, pad DREF can be left
unconnected. If a negative bias voltage is used, the configuration shown in
be used. In this configuration, the direction of the signal current is reversed to that shown
in
achieve the best sensitivity.
For maximum freedom on bonding location, 2 outputs are available for DREF (pads 1
and 3). These are internally connected. Both outputs can be used if necessary. If only one
is used, the other can be left open.
1. Reducing the capacitance of the PIN diode. This is achieved by proper choice of PIN
2. Reducing the parasitics around the input pad. This is achieved by placing the PIN
Fig 3. The PIN diode connected between
Figure
diode and typically a high reverse voltage.
diode as close as possible to the TIA.
C2
470 pF
CC
the input and pad DREF
3. It is essential that in these applications, the PIN diode bias voltage is filtered to
by a low-pass filter comprising internal resistor R
I
PD
IPHOTO
DREF
Section
1 or 3
2
Rev. 01 — 2 May 2005
7.3.
R DREF
TZA3026
300
V
CC
4 or 17
SDH/SONET STM4/OC12 transimpedance amplifier
001aac619
Fig 4. The PIN diode connected between
bias voltage
DREF
negative
the input and a negative supply
voltage
IPHOTO
is measured and sourced at pad
I
PD
DREF
DREF
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
and external capacitor C2
1 or 3
2
Figure 3
R DREF
TZA3026
300
TZA3026
V
shows the PIN
CC
Figure 4
4 or 17
001aac620
5 of 15
can