that the mixer delivers the required performance for each communication band. Although the noise figure is around 14.7 and 12.7 dB for 940 MHz (GSM) and 1.8 GHz (DCS), respectively; it rises to 18.8 dB for 2.44 GHz (Bluetooth). The noise performance is adequate for GSM and DCS standards. One can consider the noise figure for the Bluetooth frequency to be high; but the overall receiver noise figures can be as high as 40 dB for Bluetooth applications [10], and hence the simulated mixer noise figure will not affect the system noise budget very much if it is used in such a Bluetooth receiver.The IIP3 simulations prove that the L match gives better results compared to the inductive match. The minimum simulated IIP3 is Ϫ4.3 dBm at 1.54 GHz, and the maximum IIP3 achieved is 2.8 dBm at 2.44 GHz. Within these extremes, the mixer linearity performance remains satisfactory for the standards with very stringent IIP3 requirements such as GSM (900 MHz) and DCS (1800 MHz). CONCLUSIONThe wideband operation capability of the conventional mixers is discussed in this Letter. The wideband characteristics of the mixers are investigated with the use of two different types of input matching circuits. The effects of the input matching and the major performance parameters of the mixers are simulated, and the results are plotted for the overall frequency range, 940 MHz-2.5 GHz. It is worth noting that the performance drops in both of the mixers as the frequency increases, but this drop does not affect the receiver system, because the mixer exhibits good characteristics for each communication standard, and remains in line with the requirements. As a result the multiband operation of a CMOS mixer for several communication standards is expected in the near future, because the circuit performance is enhanced by the developments in the device technologies and the circuit design techniques. Once there are wideband LNAs and VCOs operating the mixers in multiband applications will be the next step.

Experimental research on the influence of a transistor amplifier on the noise power value of a passive resistor was performed. An expression for the noise temperature cooling using an attenuator–amplifier circuit is proposed, avoiding physical cooling. A significant deviation of the electromagnetic radiation value from the linear characteristics of a passive resistor is obtained into a given operation bandwidth of the amplifier for relatively small attenuation values and as a function of the input return losses. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 423–427, 2001.

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