TZA3043 Просмотр технического описания (PDF) - Philips Electronics
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TZA3043 Datasheet PDF : 28 Pages
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Philips Semiconductors
Gigabit Ethernet/Fibre Channel
transimpedance amplifier
Product specification
TZA3043; TZA3043B
PIN diode bias voltage DREF
The transimpedance amplifier together with the PIN diode
determines the performance of an optical receiver for a
large extent. Especially how the PIN diode is connected to
the input and the layout around the input pin influence the
key parameters like sensitivity, the bandwidth and the
Power Supply Rejection Ratio (PSRR) of a
transimpedance amplifier. The total capacitance at the
input pin is critical to obtain the highest sensitivity. It should
be kept to a minimum by reducing the capacitance of the
PIN diode and the parasitics around the input pin. The
PIN diode should be placed very close to the IC to reduce
the parasitics. Because the capacitance of the PIN diode
depends on the reverse voltage across it, the reverse
voltage should be chosen as high as possible.
The PIN diode can be connected to the input in two ways
as shown in Figs 7 and 8. In Fig.7 the PIN diode is
connected between pins DREF and IPhoto. Pin DREF
provides an easy bias voltage for the PIN diode. The
voltage at DREF is derived from VCC by a low-pass filter.
The low-pass filter consisting of the internal resistors
R1, R2, C1 and the external capacitor C2 rejects the
supply voltage noise. The external capacitor C2 should be
equal or larger then 1 nF for a high PSRR.
The reverse voltage across the PIN diode is 4.18 V
(5 − 0.82 V) for 5 V supply or 2.48 V (3.3 − 0.82 V) for
3.3 V supply.
It is preferable to connect the cathode of the PIN diode to
a higher voltage then VCC when such a voltage source is
available on the board. In this case pin DREF can be left
unconnected. When a negative supply voltage is available,
the configuration in Fig.8 can be used. It should be noted
that in this case the direction of the signal current is
reversed compared to the Fig.7. Proper filtering of the bias
voltage for the PIN diode is essential to achieve the
highest sensitivity level.
C2
1 nF
VCC
R2
DREF 1 125 Ω
Ii
R1 8
125 Ω
C1
10 pF
3
IPhoto
TZA3043
MGU103
VCC
R2
DREF 1 125 Ω
R1 8
125 Ω
C1
10 pF
IPhoto 3
Ii
TZA3043
negative supply voltage
MGU104
Fig.7 The PIN diode connected between the input
and pin DREF.
Fig.8 The PIN diode connected between the input
and a negative supply voltage.
2002 Sep 06
6
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