April 18
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S
ensors
itance effects. They also have recognized lim-
itations in terms of the range they can achieve.
This means that they are not suitable for
application scenarios where an air gap will
be present. In contrast, a mutual capacitance
arrangement has two separate electrodes and
detection is based on a decrease in electrode
force lines between them as the user finger
comes closer. This methodology, provided
that it is accompanied by good signal condi-
tioning, supports longer range operation and
is not impacted by parasitic capacitance to the
same extent as self-capacitance. As a result, it
is better able to deal with air gaps and inher-
ently noisy application environments.
Using a mutual capacitance approach allows
automotive engineers to deploy touch sensors
that can serve a number of different purposes.
The heightened sensitivity means that they can
be utilized not just for touch but in proximity
sensing, for instance. Figure 2 describes its use
in a smart key vehicle entry application, where
the driver is able to unlock the car door with-
out having to come into contact with the door
handle, through a change in capacitance being
determined from some distance away. Figure
3 shows how this type of sensing system may
also be applied equally well to a power window
lifter control panel application. The nature of
the cabin design means the protective cover
that the vehicle occupant touches is not likely
to be in direct contact with the PCB on which
the sensor is mounted therefore leaving a size-
able air gap. Via a mutual capacitance sensor
arrangement, the need to fill this gap with a
light guide (along with complex and expensive
to implement optical bonding) can be avoided.
The result can be a more streamlined and
cost-effective system solution.
Advanced capacitance-to-digital converter LSI
technology with industry-leading dynamic
range from companies like ON Semicon-
ductor can support significant performance
improvements in capacitance touch sensors
and thereby enhance their operation in auto-
motive applications. Designed for use with
mutual capacitance touch sensors, ON Semi-
conductor LC717A30UJ sets new standards in
relation to touch sensitivity thanks to its para-
sitic capacitance cancellation mechanism.
It also has built-in noise rejection capabilities
that help to mitigate the effects of electromag-
netic interference often present in an auto-
motive surrounding. This LSI can support
the detection of capacitance changes down to
femto-Farad (fF) levels, with a range of up to
150 mm being attained. As a result of this, it is
not just equipped to deal with conventional
touch functionality, but also proximity sens-
ing and sophisticated gesture recognition. In
addition, it means that this device is able to
operate when there is an airgap between the
sensor/PCB and the protective cover. The
need for inclusion of a light guide in the user
interface design is thereby eliminated, allow-
ing marked reductions in the bill of materials
costs to be realized.
The LC717A30UJ has eight capacitance sens-
ing input channels, making it highly suited to
inclusion within systems that require an array
of switches. Among its other features are an
analog-to-digital converter for data transla-
tion, a dual-stage amplifier for determining
capacitance changes on the analog outputs
and an integrated multiplexer for input chan-
nel selection. I2C and SPI serial interfaces can
be selected from, depending on the specific
application requirements of the system. Fur-
thermore, this highly robust AEC-Q100 com-
pliant IC has a built-in automatic calibration
function. This optimizes and self-calibrates
the touch sensor system with regard to the
characteristics of the electrode, as well as line
capacitance and the surrounding environ-
ment. It simplifies the installation process and
maximizes the effectiveness of the user inter-
face in-situ, presenting the industry with a
single chip touch/proximity sensing solution
that is both accurate and reliable.
n
Figure 2. Use of mutual capacitance sensing in a smart key application
Figure 3. Mutual capacitance sensing applied to a power window lifter
control where an air gap is present.
Wibu-Systems: CodeMeter provides
secure storage for SGX native enclaves
Wibu-Systems has successfully completed the
Intel Software Guard Extensions (Intel SGX)
enablement process for CodeMeter on Win-
dows platforms. CodeMeter is a technology
that is laser-focused on the automatic or man-
ual protection of software, firmware and data.
It combines the latest hacker-proof encryption
methods with secure hardware, software, or
cloud elements where encryption keys as well as
license and entitlement rights are safely stored.
MACOM and STMicroelectronics to bring
GaN on Silicon to RF applications
MACOM and STMicroelectronics announced
an agreement to develop GaN on Silicon wafers
to be manufactured by ST for MACOM’s use
across an array of RF applications. While
expanding MACOM’s source of supply, the
agreement also grants to ST the right to man-
ufacture and sell its own GaN on Silicon prod-
ucts in RF markets outside of mobile phone,
wireless basestation and related commercial
telecom infrastructure applications.
Mouser: Renesas’ latest versatile, low-power
RX130 32-bit MCUs now shipping
Mouser Electronics is now stocking the RX130
Group of 32-bit microcontrollers from Rene-
sas Electronics.With a new capacitive touch IP
with improved sensitivity and robustness, the
RX130 microcontrollers are ideal for devices
designed with nontraditional touch materials
or required to operate in wet or dirty envi-
ronments, such as human machine interfaces,
household kitchen and bath, motor control,
and factory applications.
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