Digital Variable Capacitor Tunes Antenna For Maximum Efficiency
Detuning mobile antennas is easy. Just hold your cell phone or tablet in your hand or near your head. All antennas are inherently resonant devices with limited bandwidth, which doesn’t match up well with today’s wideband wireless technologies like WCDMA, HSPA, and LTE. As a result, most antennas compromise with lower radiation efficiency—unless they can be tuned.
Tuning is essential to getting the most power and efficiency out of any given antenna. The impedance matching circuits should be varied to optimize output even when detuning occurs. Of course, you need variable components that can be manipulated to compensate for the detuning. When it’s used in an antenna matching circuit, the Ethertronics EtherChip 1.0 digitally tunable capacitor can easily tune for maximum output despite external detuning influences.
Tuning the antenna to the environment increases efficiency. Manufacturers then can more easily meet the CTIA’s Total Isotropic Sensitivity/Total Radiated Power (TIS/TRP) test procedures. TIS/TRP measures the 3D radiation capability of a given antenna.
The 4-bit, 16-state EtherChip operates from 100 MHz to 3.0 GHz (see the figure). The basic tuning range is 0.85 to 3.4 pF in 0.17-pF increments—a 4-to-1 tuning ratio. It’s designed to be used in a shunt to ground configuration to tune the lower-frequency antenna. The digital control comes via an SPI port driven by the handset’s logic (lookup table, FPGA, etc.). Tuning control is open loop. Switching speed is on the order of 10 µs.
The EtherChip 1.0 is one step closer to Ethertronics’ goal to develop a fully integrated antenna front-end module (AFEM) incorporating the antenna, tuning, filters, power amplifier, and other circuitry that can further increase radiation efficiency.
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