From signal dropout, to shrinking antenna sizes, to the proliferation of wireless bands and standards, today’s smartphones face a range of challenges. To solve these issues, wireless designers are turning to new radio frequency (RF) microelectromechanical system (MEMS) solutions that use digital capacitor technology to dynamically tune antennas.
WiSpry Inc.—a company recently acquired by AAC Technologies Holdings Inc.—has been shipping a line of MEMS-based tunable capacitor devices that have gained acceptance in recent years. Samsung’s Focus Flash Windows smartphone, which went on sale in 2011, was the first smartphone found to include a WiSpry RF MEMS device, according to a dissection conducted by the IHS Teardown Analysis Service. This marked the first time such a part was detected in a smartphone.
WiSpry tunable digital capacitor technology is a method for dynamically tuning antennas, matching networks, integrating tunable filters, tunable duplexers and fully-tunable power amplifiers. The company’s line of tunable RF capacitor chips contains three or four tunable RF series capacitors. A single WiSpry device can be used to produce a tunable inductor/capacitor (LC) network. Larger capacitance values can be achieved by combining capacitors.
An LC circuit, also known as a resonant circuit, is an electric circuit that links together an inductor and a capacitor. The circuit can act as an electrical resonator, which can store energy oscillating at the circuit’s resonant frequency.
LC circuits can generate signals at a particular frequency, or may pick out a signal at a specific frequency. Because of this, they play a key role in wireless systems, employed in oscillators, filters, tuners and frequency mixers.
The use of RF MEMS capacitor chips can help solve many challenges related to cellphones.
One of these issues is the so-called “death grip” that reportedly affected the iPhone 4. Some users reported that when the smartphone was held in a certain manner, cellular Internet signal strength would drop out. The WiSpry solution can mitigate this issue by improving reception.
Furthermore, RF MEMS capacitors enable cellphones to integrate smaller antennas that are just as efficient as larger ones. This can allow the design of thinner phones. The improved antenna efficiency also can allow network operators to save money as they deploy new wireless infrastructure. This could amount to hundreds of millions of dollars in savings, according to IHS.
Beyond reception issues, a major reason why cellphone makers are adopting RF MEMS is their capability to efficiently implement the proliferating number of standards and rising data usage of cellphones. With cellphones spreading to more regions of the world, more standards are being employed for their use.
A conventional RF architecture in a phone supports multiple standards by using multiple RF paths, each working in parallel. This drives up the number of components, power consumption and cost of the phone each time a new standard is integrated. The RF MEMS capacitor solution allows cellphones to gain capability while constraining increases in size, cost and power consumption.