In order to reduce the size of a wireless system, we propose a design theory for the broadband impedance matching circuit which connects an electrically small antenna (ESA) to a semiconductor amplifier. We confirmed its validity for the case of connection between a small slot loop antenna with a small radiation resistance of Ra =0.776 Ω and a semiconductor amplifier with high input impedance of ZL =321-j871 Ω with the aid of the simulations by the electrical circuits using transmission lines as well as the electromagnetic field (EM field) simulator. We also made experiments on this antenna with matching circuits using high temperature superconductor YBCO thin films on MgO substrates.

A fully integrated RF front-end for W-CDMA applications including a low noise amplifier, a down conversion mixer, a digitally programmable gain amplifier, an on-chip VCO, and a fractional-N frequency synthesizer is designed using a 0.35-µm CMOS process. A multi-stage ring shaped on-chip LC-VCO exhibiting bandpass characteristics overcomes the limitation of low-Q components in the tank circuits and improves the phase noise performance. The measured phase noise of the on-chip VCO is -134 dBc/Hz at 1 MHz offset. The receiver RF front-end achieves a NF of 3.5 dB, an IIP3 of -16 dBm, and a maximum gain of 80 dB. The receiver consumes 52 mA with a 3-V supply and occupies only 2 mm2 die area with minimal external components.

A broadband RF front-end having a direct conversion architecture has been developed. The RF front-end consists of two broadband quadrature mixers, a multi-band local oscillator, and a broadband low-noise variable gain amplifier (LNVGA). The mixer achieves broadband characteristics through the incorporation of an in-phase power divider and a 45-degree power divider. The in-phase power divider achieves broadband characteristics through the addition of a compensation capacitor. The 45-degree power divider achieves broadband phase characteristics through the addition of a compensation capacitor and a compensation resistor. The local oscillator, which is composed of two VCOs, two frequency dividers, and four switches, can cover three systems including one FDD system. The LNVGA achieves its broadband characteristics without the use of reactance elements, such as inductors or capacitors. In a trial demonstration, when the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a demodulator experimentally demonstrated an amplitude balance of less than 1.6 dB and a quadrature phase error of less than 3 degrees. When the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a modulator demonstrated an image ratio of less than -30 dBc. The local oscillator demonstrated multi-band characteristics, which are able to cover the target frequencies for three systems (PDC, PHS, 2.4 GHz WLAN). From 900 MHz to 2.5 GHz, the amplifier shows a noise figure of less than 2.1 dB and a gain of 28 1.6 dB.