| High-performance radios continue to stimulate the demand for more highly optimized RF circuits. While advances in semiconductor technology have enabled monolithic integration of RF circuitry, many RF circuit design techniques are based on ad-hoc practice, often resulting in non-optimum designs.; The minimum noise figure (NF) of a bipolar transistor has a global minima which depends solely on the collector current density, while the optimum source impedance is set by the device area. Therefore, obtaining minimum NF simultaneously with maximum power transfer is possible. The shallow nature of the global minima makes the NF insensitive to bias current variations, which is required for multi-mode designs. Furthermore, the optimum current density scales linearly with frequency while the optimum source impedance remains constant if the device area is scaled inversely with frequency. As a result, transforming the design from one frequency to another is achieved by simple circuit scaling. These theoretical results have been applied to low-noise amplifier (LNA) and active mixer designs, and verified by constructing a 1.8 GHz frequency-scaled SiGe bipolar test chip. The measured LNA NF is 1.3 dB, while the double-balanced mixer achieves a NF of 6.0 dB.; A new class of low-voltage current-mode programmable filters is well suited for highly integrated receivers because of their high dynamic-range. These filters operate from a supply voltage of 1.5 V while their compression point depends on the supply current. The cutoff frequency, ω0, depends on the product of two bias currents while the quality factor, Q, depends on the ratio, therefore, independent ω0- Q tuning is achieved. Two I/Q 1 MHz Bessel low-pass filters have been fabricated in a 0.8 μm CMOS process. These filters achieve a 1% total harmonic distortion dynamic-range of 81 dB and a NF of 9.3 dB, assuming a 1k Ω source. The measured in-band, input-referred second-order and third-order intercept points are +52.5 dBm and +30.5 dBm, respectively. Power consumption per pole is 0.9 mW.; A 1.5 GHz homodyne receiver, constructed from the elements above, achieves a NF of 1.2 dB, and a spurious-free dynamic range of 59 dB, which is limited by the front-end. |
