tza3013bu-n3 NXP Semiconductors, tza3013bu-n3 Datasheet - Page 6

• Manufacturer Part Number: tza3013bu-n3
• Description: Sdh/sonet Stm16/oc48 Transimpedance Amplifier
• Manufacturer: NXP Semiconductors

Philips Semiconductors
PIN diode bias voltage DREF
The performance of an optical receiver is largely
determined by the combined effect of the transimpedance
amplifier and the PIN diode. In particular, the method used
to connect the PIN diode to the input and the layout around
the input pad strongly influences the main parameters of a
transimpedance amplifier, such as sensitivity, bandwidth,
and PSRR. Sensitivity is most affected by the value of the
total capacitance at the input pad. Therefore, to obtain the
highest possible sensitivity requires the value of total
capacitance to be as low as possible by reducing the
capacitance of the PIN diode and the parasitics around the
input pad. To minimize parasitics, the PIN diode should be
placed as close as physically possible to the IC. The
capacitance of the PIN diode can be reduced by making
the value of reverse voltage across it as high as possible.
The PIN diode can be connected to the input in two ways.
Figure 5 shows the PIN diode connected between
pads DREF and IN.
2001 Feb 26
handbook, halfpage
SDH/SONET STM16/OC48
transimpedance amplifier
Fig.5
100 pF
The PIN diode connected between the input
and pad DREF.
C2
I i
DREF
IN
1
2
270
R1
V CC
TZA3013
30
MGU120
6
Pad DREF provides an easy bias voltage for the
PIN diode. The voltage at DREF is derived from V
low-pass filter comprising internal resistor R1 and external
capacitor C2 which decouples any supply voltage noise.
The value of external capacitor C2 affects the value of
PSRR and should have a minimum value of 100 pF.
Increasing this value increases the value of PSRR.
For a supply voltage of 3.3 V, the reverse voltage across
the PIN diode is 2.438 V (3.3 V
to connect the cathode of the PIN diode to a voltage higher
than V
pad DREF unconnected. If a negative supply voltage is
available, the configuration shown in Fig.6 can be used.
It should be noted that in this configuration, the direction of
the signal current is reversed to that shown in Fig.5. It is
essential that the PIN diode bias voltage is correctly
filtered to achieve the highest possible level of sensitivity.
handbook, halfpage
Fig.6
CC
negative supply
if there is one available on the PCB, leaving
The PIN diode connected between the input
and a negative supply voltage.
I i
DREF
IN
TZA3013A; TZA3013B
1
2
270
V CC
TZA3013
30
0.862 V). It is preferable
MGT103
Product specification
CC
by a