Full length article: Emerging applications of wavelets: A review

A study of the limitations of active CMOS filters at high frequencies suggests automatic means to compensate imperfections in the filter response introduced by active devices. The effects of nonzero FET output conductance, limited frequency response and noise on the filter characteristics, and dynamic range are analyzed, particularly for filters with high Q components. These are used to demonstrate a 3- mu m CMOS realization of a fourth-order bandpass filter with a 250-kHz passband centered at 12.5 MHz. The filter demonstrates that the maximum frequency of filter operation is not as seriously limited by device f/sub T/ as was previously thought, but that automatic means may be used to tune out the imperfections introduced in the filter elements by the limited voltage gain and frequency response of transistors. >

CMOS active filter design at very high frequencies

A low voltage (1 V), low-power (100 mu W), and low-frequency (9 kHz) fifth-order fully integrated active low-pass filter (LPF) using a bipolar technology is described. Novel highly linear transconductors consisting of N emitter-coupled pairs were designed for low-voltage operation. The linear input range is expanded to about 100 mV/sub p-p/ at 1% error with N=4, which is about twice that of the conventional linearization technique. The filter is basically a gyrator-capacitor type, in which gyrators are implemented by using the linearized transconductors. Large time constants were realized with very low current (540 nA/transconductor) owing to the high transconductance-to-operating-current ratio of the linearized transconductors. Measured results show a passband ripple of 1.5 dB, a minimum stopband rejection of 70 dB, and a dynamic range of 56 dB, despite a very high nominal impedance (400 k Omega ). Practical limitations of this approach are also discussed, such as the sensitivity of the linearized transconductors against process variations, noise, and frequency limitations. >

Realization of a 1-V active filter using a linearization technique employing plurality of emitter-coupled pairs

A `triode transconductor´ fully differential transconductance element for use in continuous-time CMOS integrated filters is proposed. It is based on a common-source pair of triodemode MOS transistors. Preliminary experimental results from breadboarded transconductors and complete filters show good distortion performance. Several practical advantages are claimed over previous approaches.

CMOS triode transconductor for continuous-time active integrated filters

A single-chip gyrator filter for separating the components of the video signal in a TV receiver is described which is suitable for mass production in a standard bipolar process (f/SUB T//spl ap/400 MHz). The 11 mm/SUP 2/ filter chip operates at frequencies up to 10 MHz, requires no tuning or alignment and has Q-factors which are stable with temperature. The IC contains an automatic tuning system which tunes the five resonators of the filter by aligning an auxiliary gyrator resonator with the crystal oscillator present in the color decoder of a TV receiver. Problems of matching the frequencies of the individual gyrator resonators are discussed, showing how alignment accuracy of 0.5 percent can be obtained when resistivities and specific capacitances have production spreads of at least 10 percent. Various gyrator circuit configurations are given which minimize the circuit complexity and, hence, the chip area. Computer aided design techniques for the filter using geometrically scaled models and macromodeling are presented and it is shown how a complete simulation of the chip led to a significant improvement in bandstop performance. Finally, the measured responses are presented and the filter performance is discussed in the light of present-day requirements.

Gyrator video filter IC with automatic tuning

An experimental single-chip silicon integrated-circuit filter is described for use in color television receivers. It comprises five gyrator resonators operating in the range 4-6 MHz. This chip provides all the selectivity required to separate the sound, luminance, and chrominance components from the composite video signal, and is tuned by a single bias potential applied to the p-n junction capacitors on the chip. The chip replaces an equivalent LC filter of about 20 discrete components (coils, capacitors, and resistors) which are bulky, are relatively expensive, and suffer from the need for individual screening and alignment. The theory of gyrators related to providing fully integrated selectivity at high frequency is outlined. Performance boundaries in terms of Q-factor, frequency setting accuracy, noise, distortion, and temperature are considered. Design aspects are discussed, first for a gyrator and then for the complete experimental filter chip.

K.W. Moulding

Papers

A fully integrated five-gyrator filter at video frequencies