RF Transceivers for Keyless Entry Systems
The term
“transceiver” is a portmanteau of “transmitter” and “receiver”, describing a device that can
perform both of these functions. Radio frequency (RF) transceivers are used to transmit and
receive information wirelessly via radio waves. Frequency abbreviations are used to denote the
particular range of wavelengths in which an RF tranceiver/transmitter/receiver is designed to
operate. For example, UHF (ultra high frequency) is designated as the frequency band from 300MHz
to 3GHz, and LF (low frequency) includes the 30kHz to 300kHz range. Therefore a UHF transceiver
will communicate on one or more frequencies within the UHF band, an LF tranceiver within the LF
band, and so on.
Microcontrollers for Keyless Entry Systems
Microcontrollers are similar
to processors in that they perform computational functions and carry out the instructions of a
computer program. A microcontroller, however, is often used for embedded applications – as
opposed to central processing units (CPUs) which are designed more commonly for general-purpose
computing. Furthermore, microcontrollers are meant to reduce size and cost by including
integrated peripherals such as flash memory, analog-to-digital converters (ADCs),
digital-to-analog converters (DACs), device drivers, transceivers for various communications
protocols, and more.
Analog Front End ICs for Keyless Entry Systems
Analog front-end (AFE) is a
somewhat generic term for the analog portion of an electronic system. Though they may vary in
form and function, all AFEs provide some sort of analog signal conditioning. They are typically
followed by A/D conversion to produce a signal that is useable by a processor. In the case of a
passive keyless entry system, an AFE may be used to filter, demodulate, and/or amplify the input
signal received from an attached LC antenna, as well transmit RF signals by driving the antenna
instead.
EEPROM for Keyless Entry Systems
EEPROM stands for
Electronically Erasable Programmable Read-Only Memory. It is non-volatile type of memory,
meaning that a power source is not required to preserve stored information. EEPROM and flash
memory share many of the same qualities – in fact, flash memory is often considered an advanced
form of EEPROM. However, one of the largest functional distinctions between the two lies in how
the memory can be erased: unlike flash, EEPROM is erasable at a more precise, byte-wise level.
For this reason among others, EEPROM continues to see industry use in applications that must
store small amounts of non-volatile data.
Processors for Keyless Entry Systems
The term "processor"
refers to an electronic device that performs computational functions and carries out the
instructions of a stored program. Other terms for processor are microprocessor, central
processing unit, and digital signal processor. Essentially, the processor refers to "the brains
of a computer."
LIN Transceivers for Keyless Entry Systems
LIN (Local
Interconnect Network) is a vehicle network protocol for communication between automotive
components. Inexpensive and relatively simple to implement, a LIN network uses a broadcast
topology with a single master – typically an MCU – and up to 12 slave devices. As such, it is
often used for networking small subsystems, with the master device connecting the subsystem to
the vehicle’s main bus line, such as a CAN bus.
CAN Transceivers for Keyless Entry Systems
CAN is an acronym for
Controller Area Network and refers to a fault-tolerant communications protocol that is flexible
for system design, supports multiple network topologies, and has become a de facto standard for
high integrity serial communications in industrial and automotive embedded applications. In a
CAN network, several short pieces of data like a motor’s run status, temperature, or RPM is
broadcast over the entire network at up to 1 megabit per second (Mbps.) CAN is meant for
applications that have to report and consume numerous but small pieces of data consistently
among nodes and has the ability to self-diagnose and repair data errors. CAN is well-suited to
environments with machinery, since CAN is designed to be reliable in rugged environments that
include interference or introduce noise. CAN is also well-suited to the transportation industry.
DC/DC Converters for Keyless Entry Systems
DC/DC regulators
are circuits that convert DC voltage from one level to another and maintain that voltage at a
constant level. Electronic systems often have several sub-circuits, each with its own voltage
level requirement that may be higher or lower than the main power supply. Step-up (boost)
converters raise a voltage to a higher level, while step-down (buck) converters lower it. Some
DC/DC converter types can raise or lower voltage, such as "buck-boost" converters. DC/DC
converters may offer options such as multiple softstart levels, undervoltage lockout, protection
against overvoltage and undervoltage, and programmable short-circuit protection. All of these
devices are considered to be in the same category of integrated chips, typically categorized as
power management devices.
Low-Dropout Regulators for Keyless Entry Systems
A Low Drop Out (voltage)
Regulator is a voltage regulator that automatically maintains a constant voltage level and
features a low potential at below which it can no longer reliably regulate. LDOs stabilize input
or supply voltages. LDOs are instrumental in enabling the power-efficient portables in use today
because they enable very low minimum operating voltages.
Buck/Boost Regulators for Keyless Entry Systems
A buck
converter is a power efficient voltage step-down converter that changes a higher voltage to a
lower voltage. Whereas a linear regulator can achieve the same purpose, regulators can waste
more energy via conversion of excess energy to heat. For this reason, a buck DC/DC converter is
the preferred choice for power-efficient designs. A DC/DC boost converter, also known as a
step-up converter, is a semiconductor device or electrical circuit that has an output DC voltage
that is greater than the DC input voltage. The amount of output current will be lower than the
source current, however. Boost converters can increase the voltage and thus reduce the total
number of battery cells required for portable applications.
Step-Down Regulators for Keyless Entry Systems
A step-down
(buck) regulator maintains a constant output DC voltage level that is lower than its input DC
voltage while preserving polarity. Electronic systems often have several sub-circuits, each with
its own voltage level requirement that may be lower than the main power supply, therefore
step-down regulators may be required. The switching regulator offers the advantages of high
power conversion efficiency and increased design flexibility; multiple output voltages of
different polarities can be generated from a single input voltage. Since the output voltage of
the buck is lower than the input voltage, it follows that the output current must be higher than
the input current.
