Detailed Description
The MAX40658 and MAX40659 transimpedance amplifiers
are designed for optical distance measurement applications
and are comprised of a transimpedance amplifier and a
voltage amplifier/output buffer.
Gain Stage 1
The signal current at the input flows into the summing
node of a high-gain transimpedance amplifier. Shunt
feedback through the feedback resistor converts this
current into a voltage. An internal Schottky diode clamps
input currents up to 100mA (see the Typical Application
Circuits). Bypass CCAP (internally connected to the cathode
of the internal Schottky diode) with a 1µF capacitor. An
external Schottky diode may be added for increased
clamping current capability.
Gain Stage 2
The second gain stage provides additional gain and
converts the transimpedance amplifier single-ended
output into a differential signal. Two different versions
are available (MAX40658 and MAX40659), each with a
different voltage amplifier gain.
This stage is designed to drive a 150Ω differential
load between OUT+ and OUT-. For optimum supply
noise rejection, the outputs should be terminated with a
differential load. The single-ended outputs do not drive
a DC-coupled grounded load. The outputs should be
AC-coupled or terminated to V
CC
. If a single-ended
output is required, both the used and unused outputs
should be terminated in a similar manner.
Oset Adjustment
The OFFSET input accepts an input current that may be
used to adjust the input offset current of the TIA. Current
flowing into the pin yields a negative offset equivalent
to I
OSIN
/4, where I
OSIN
is the current flowing into the
OFFSET pin. The OFFSET pin is biased to the same
voltage as the IN pin.
Applications Information
Photodiode
Noise performance and bandwidth are adversely affected
by capacitance on the TIA input node. Select a low-
capacitance photodiode to minimize the total input
capacitance on this pin. The TIA is optimized for 0.5pF
of capacitance on the input. Assembling the TIA in die
form using chip and wire technology provides the lowest
capacitance input and the best possible performance.
Supply Filter
Sensitive optical receivers require wide-band power supply
decoupling. Power supply bypassing should provide low
impedance between V
CC
and ground for frequencies
between 10kHz and 700MHz. Isolate the amplifier from
noise sources with LC supply filters and shielding. Place
a supply filter as close to the amplifier as possible.
ESD Protection
The MAX40658/MAX40659 TIAs do not contain ESD
protection diodes on the analog input (IN). This is to
ensure maximum bandwidth and dynamic performance.
Care must be taken when handling the package to ensure
proper operation.
Refer to Maxim Application Note 639 and Application
Note 651 for more details.
www.maximintegrated.com
Maxim Integrated
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MAX40658/MAX40659 Transimpedance Amplier with 100mA Input
Current Clamp for LiDAR Applications
