MAX3267 MAXIM [Maxim Integrated Products], MAX3267 Datasheet - Page 7

• Manufacturer Part Number: MAX3267
• Description: 1.25Gbps/2.5Gbps, 3V to 5.5V, Low-Noise Transimpedance Preamplifiers for LANs
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 5. Optical Power Relations
Table 1. Optical Power Relations
The MAX3266 has high gain, which limits the output
when the input signal exceeds 30µAp-p (40µAp-p for
MAX3267). The MAX3266 operates in a linear range for
inputs not exceeding:
Use good high-frequency design and layout tech-
niques. The use of a multilayer circuit board with sepa-
rate ground and power planes is recommended.
Connect the GND pins to the ground plane with the
shortest possible traces.
Average Power
Extinction Ratio
Optical Power
of a “1”
Optical Power
of a “0”
Signal
Amplitude
PARAMETER
Linear Range
P
AVE
PO
PI
1.25Gbps/2.5Gbps, 3V to 5.5V, Low-Noise
SYMBOL
_______________________________________________________________________________________
P
P
10
Transimpedance Preamplifiers for LANs
P1
P0
AVE
r
IN
e
log
TIME
Layout Considerations
30
P
r
P1 = 2P
P0 = 2P
P
e
AVE
IN
Optical Linear Range
2
= P1/P0
= P1 - P0
= 2P
A r
r
= (P0 + P1)/2
e
e
AVE
AVE
AVE
RELATION
1
(r
/ (r
(r
1
e
e
) / (r
e
1000
) / (r
+ 1)
e
e
+ 1)
+ 1)
dBm
Noise performance and bandwidth will be adversely
affected by capacitance at the IN pin. Minimize capaci-
tance on this pin and select a low-capacitance photodi-
ode. Assembling the MAX3266 in die form using chip
and wire technology provides the best possible perform-
ance. Figure 6 shows a suggested layout for a TO
header.
The SO package version of the MAX3266 is offered as
an easy way to characterize the circuit and become
familiar with the circuit’s operation, but it does not offer
optimum performance. When using the SO version of
the MAX3266, the package capacitance adds approxi-
mately 0.3pF at the input. The PC board between the
MAX3266 input and the photodiode also adds parasitic
capacitance. Keep the input line short, and remove
power and ground planes beneath it.
Supply voltage noise at the cathode of the photodiode
produces a current I = C
receiver sensitivity (C
tance.) The filter resistor of the MAX3266, combined
with an external capacitor, can be used to reduce this
noise (refer to the Typical Application Circuit ). Current
generated by supply noise voltage is divided between
C
noise is (assuming the filter capacitor is much larger
than the photodiode capacitance):
If the amount of tolerable noise is known, the filter
capacitor can be easily selected:
For example, with maximum noise voltage = 100mVp-p,
C
be 100nA (1/2 of the MAX3266’s input noise):
For high current density and reliable operation, the
MAX3266 uses gold metalization. Connections to the
die should be made with gold wire only, using ball
bonding techniques. Wedge bonding is not recom-
mended. Die thickness is typically 15 mils (0.375mm).
C
FILTER
PD
FILTER
= 0.85pF, R
I
C
NOISE
FILTER
and C
= (100mV)(0.85pF) / (1500Ω)(100nA) = 570pF
= (V
= (V
PD
FILTER
NOISE
. The input noise current due to supply
NOISE
)(C
= 1.5kΩ, and I
PD
)(C
PD
PD
is the photodiode capaci-
PD
) / (R
∆V/∆t, which reduces the
) / (R
Photodiode Filter
FILTER
FILTER
NOISE
Wire Bonding
)(C
)(I
FILTER
NOISE
selected to
)
)
7