Low Cost Embedded Accurate 6 GHz RF Frequency Counter

Abstract

Speed, portability and quality. These are all attributes that manufacturers are
striving to achieve. The demand for speed is making wireless frequencies increase
with a steady pace. The demand for portability is filling the world with high speed
wireless devices that are expecting their data fast and without errors. The demand
for quality is met by making efficient ways of testing products before reaching the
market to ensure faulty devices never reaches the consumer.
A common way of testing product is to build a fixture containing means of
connecting to the different interfaces of the device and running tests on them to
assure proper functionality. Since wireless products are becoming more and more
popular, carrier wave frequencies and wireless output power are things in need of
testing.
The scope of this thesis has been to, with easily accessible, commercial components,
implement a prototype design of a low cost, accurate frequency counter
capable of measuring frequencies of signals up to 6 GHz. The project includes
the construction of a 4 layer printed circuit board to implement a prescaler to
bring the high frequencies down to more manageable frequencies. The prescaler
includes the means of attenuating strong signals and amplifying weak signals in
order to ensure the capability of covering as many use cases as possible from measuring
a wireless signal received from an antenna to measuring a high power signal
ready to be transmitted. The divided signal is then processed by a microcontroller
and the input frequency is calculated. The prototype can be supplied via a USB
connection. All the specification requirements were met and this thesis provides a
stable base to further develop a low cost, embedded, accurate 6 GHz RF frequency
counter.

Popular Abstract

If it can be built, you can build it. That has been a motto of mine for quite
some time now. And it was this kind of thought that sprung the project leading
to this thesis work at Mikrodust AB. Mikrodust has specialized in building test
fixtures. Test fixtures are specially made fixtures for a specific product. The
fixture connects to the product through its different interfaces and runs a series
of tests on the product. This is done to assure that the product functions as it is
supposed to and that nothing has gone wrong in the manufacturing of the product.
These tests are done to assure that a faulty product does not reach the customer
but also to get statistics about what the bottlenecks of the product design are.
What is most likely to fail and what can be done to prevent it?
The rising popularity of wireless products causes the need for cost efficient,
accurate and small radio test equipment that can be integrated into a test fixture.
One example of test equipment commonly used to verify the radio signals frequency
is the frequency counter. This is used to check if the transmitted signal frequency is
within the specified limits for the protocol used. Mikrodust have previously used
a commercial frequency counter to measure the output frequency of the carrier
waves for different products. The goal of this thesis work was to investigate the
possibility for Mikrodust to implement their own frequency counter. This to save
money and to rid them from dependence of another company to make their test
fixtures. The frequency counter should be able to accurately measure frequencies
to up to 6 GHz. 6 GHz was a limit chosen by Mikrodust in order to include
the most common frequencies used in wireless communication and still have a
buer for future protocols. Mikrodust wanted the counter to be implemented on
a microcontroller that is frequently used by the company. However to be able to
sample such a high frequency signal in a microcontroller the signal must first be
divided down to a lower frequency. This is done in order for the slower components
in the microcontroller to be able to detect the signal. The primary task in this
thesis work was to find a suitable frequency divider.
After having compared a variety of solutions taking noise, power consumption
and cost into consideration a suitable candidate were chosen to be used in the
prototype design. When the divider was chosen began the work of implementing a
design to making the circuit run. A printed circuit board was designed including
features such as a programmable front-end, capable of attenuating and amplifying
signals to the ideal level for the divider. The design also features a power supply
solution which allows the board to be supplied via a common USB port. The
front end and divider are controlled by the microcontroller, which can set the
division to anything from 32 to 1048575. The output of the prescaler circuit is
a square wave with the divided frequency, which can easily be detected by the
microcontroller. The microcontroller interrupts every N'th period (where N can
be chosen to any positive integer) of the signal and counts the number of clock
cycles between these instances. In this way an average period time of the signal can
be found and with that the frequency. When the divided frequency is known the
microcontroller simply multiplies with the division ratio and now the undivided
frequency is known. When a working prototype was done the evaluation began.
The results were good, the prototype succeed to meet all specifications. And will
provide a solid base to further develop to reach the goal, a low cost, embedded,
accurate, 6 GHz RF frequency counter.

• author: Hellman, Linus
• supervisor: Markus Törmänen
• organization: Department of Electrical and Information Technology
• course: EITM01 20171
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: RF, 6 GHz, Frequency counter, Prescaler
• report number: LU/LTH-EIT 2017-571
• language: English
• id: 8908963
• date added to LUP: 2017-06-01 15:04:58
• date last changed: 2017-06-01 15:04:58