AVX has developed a 'supercapacitor' that can extend the effective talk time of battery-powered mobile phones and data modems by more than 25%.
Based on the BestCap technology launched last year, the SlimCap is 2mm thick, which is enough to squeeze it into PC cards. The capacitor can support the 40 or 50mF needed by cellular radio interfaces.
AVX is now working on an even thinner version that could be used in mobile phones. By coupling a supercapacitor with a conventional battery, AVX technology development project director Scott Tripp says the ability of the capacitor to supply current at higher voltages than the battery means that a phone can survive for longer before the battery needs to be charged.
The main difference between AVX's design and other super-capacitors lies in the BestCap's ability to supply short pulses of power, such as those needed by a GSM power amplifier.
Unlike conventional capacitors, which rely on purely electronic charge separation, supercapacitors use electrochemical reactions.
Tripp said: "There are plenty of electrochemical capacitors about. We do not have the highest volumetric efficiency but where we score is in pulse applications."
The problem for most electrochemical capacitors is that they typically have high effective series resistances and are slow to respond to peak demands because most of the charge is carried by ions, not electrons.
"They lose a great deal of their capacitance under short pulse durations. Most supercapacitors are rated at one second. Many of them can lose 90% of their capacitance with short pulse widths," said Tripp.
The AVX design uses hydrogen ions to act as the charge carriers in its polymer-based design. The protons exchanged are much lighter and faster than the ions typically used in supercapacitors.
"At 1ms, it keeps 60% of its rated capacity," said Tripp. "The major application we have found so far is in GSM products such as RF modems." The company has developed a version that can fit into a PCMCIA card.
"The BestCap works in co-operation with a battery. It gives the battery a kick to give the 2A required for each classic GSM pulse of 0.5ms," said Tripp.
"The idea is to get the voltage higher than that of the battery and improve the efficiency of the PA [power amplifier]. A lot depends on the cut-off voltage of the circuit. But because it can boost the voltage, there is the possibility of extending talk time [by squeezing more useful current out of the battery.]
"You can get from 25% more up to very high levels. And in very cold conditions, the improvement in talk time is very significant."