Page 23 - EngineerIT September 2021

MEASUREMENT

rejects ambient light and dissipates little power with unlimited with an ideal TIA model with zero recovery time, the recovery time
bandwidth. The reality is that some of these qualities have would still be compromised when the AC capacitor is added. This
mutually exclusive design considerations. may be a scenario where it might make sense to consider adding
DC-coupled or DC-coupled with DC cancellation circuitry.
AC coupling versus DC coupling
If you choose AC coupling, your dynamic range is increased at Summary
the cost of recovery time when saturated. AC coupling makes LIDAR input is not a trivial topic, and there are going to be many
sense for applications that can tolerate tens of microseconds of moving parts in the design process. The signal chain is going
recovery time for the TIA. If DC coupling is selected, the recovery to be different depending on which design you choose, so it’s
rate is much faster at the cost of some or all of your dynamic important to consider all your options before choosing the one
range being lost from DC effects. DC coupling makes sense in that is best for your project. n
applications that require fast recovery and are not as sensitive
to DC effects that may inhibit dynamic range. If DC coupling About the authors
with integrated current cancellation is the chosen topology, your Noe Quintero started as applications engineer at Analog Devices
dynamic range is increased, saturation recovery speed and in 2015 and became an analogue design engineer in 2019.
channel switching are faster with the requirement of additional He has a B.Sc. in electrical engineering from San Jose State
design complexity. This topology is a requirement for automotive University and specialises in signal chain solutions. He can be
LIDAR since the need for fast recovery and more dynamic range reached at noe.quintero@analog.com.
are justified for the extra design and costs.
Simply adding an AC-coupling capacitor to the input of the Tony Pirc has a B.Sc. in electrical engineering, as well as
transimpedance amplifier in a pulsed application can harm the minors in computer engineering, physics and mathematics
performance of your system. However, trade-offs can be made to from California State University, Chico. He has a background
achieve realistic goals, depending on your needs. Not all systems in industrial automation in a manufacturing environment. He
require the best recovery times (for example industrial and supported precision amplifiers at Analog Devices.
instrumentation systems), and AC coupling can be applied to these
circuits. In cases where the TIA struggles to recover when the input For more information on Analog Devices contact Conrad Coetzee
is AC coupled, it is convenient to blame the TIA. However, even at ccoetzee@arrow.altech.co.za

STM32Cube.AI

STM32Cube.AI is an extension pack to the
popular STM32CubeMX tool enabling AI on
STM32 Arm® Cortex®-M-based microcontrollers

DIMENSION
• Quickly assess model footprint requirements
• Select and configure MCU in STM32CubeMX
• Review model layers in STM32Cube.AI

OPTIMISE
• Generate C-code for pre-trained model
• Support quantized models to reduce RAM,
flash and latency with minimal loss of accuracy
• Use light run-time libraries
• Optimize for performance

FINE TUNE
• Optimize memory allocation
• Fine control of weight mapping
• Split between internal and external memory
• Update model without full FW update

FOR MORE INFO AND DEMO KITS contact Renaldo Fibiger
on +27 83 388 6501 or rfibiger@arrow.altech.co.za