A simple modification to a one-stage op-amp for operation as a class AB amplifier leads to significant slew rate and bandwidth enhancement with essentially equal silicon area and static power dissipation requirements. Experimental results of a prototype in 0.5 /spl mu/m CMOS verify SR and bandwidth enhancement factors of almost one order of magnitude.

Simple technique using local CMFB to enhance slew rate and bandwidth of one-stage CMOS op-amps

We propose a circuit technique that enables the realization of widely programmable high-frequency active RC filters in CMOS technology. A fifth-order Chebyshev ladder filter having a digitally programmable 3-dB bandwidth (from 44 to 300 MHz) is used as a vehicle to validate our ideas. The opamp uses feedforward compensation for achieving high dc gain and wide bandwidth. The integrating resistors are realized as a series combination of a triode-operated MOSFET and a fixed polysilicon resistor. A charge-pump-based servo loop servoes the integrating resistor to a stable off-chip resistor. The principle of ldquoconstant capacitance scalingrdquo is applied to the opamp and the integrating resistors so that the shape of the frequency response is maintained when the bandwidth is scaled over a 7 times range. The filter core, designed in a 0.18-mum CMOS process, consumes 54 mW from 1.8-V supply and has a dynamic range of 56.6 dB.

Widely Programmable High-Frequency Active RC Filters in CMOS Technology

An integrated fifth-order continuous-time low-pass filter for a WiMedia ultrawideband radio receiver is described in this paper. The prototype filter is realized with a passive pole at the filter input and a fourth-order leapfrog filter in which the gm-C technique with pseudodifferential transconductors is used. The transconductors do not include internal nodes, and they are designed to have a nominal 26-dB dc gain, of which process, voltage, and temperature variations are controlled by means of a negative resistance circuit. The losses of the low-dc-gain filter integrators are already taken into account in the filter synthesis. The passband edge frequency of the implemented filter is 240 MHz in order to receive multiband-orthogonal-frequency-division-multiplexing signals using the direct-conversion topology. The voltage gain of the filter can be controlled from 9 to 43 dB in the 1-dB gain steps. The filter achieves a 7.8-nVradicHz input-referred noise density, a -8-dBV out-of-band third-order intermodulation intercept point, and a +15-dBV out-of-band second-order intermodulation intercept point. The circuit uses a 1.2-V supply and has been fabricated in a modern 65-nm CMOS technology.

A 240-MHz Low-Pass Filter With Variable Gain in 65-nm CMOS for a UWB Radio Receiver

Sensitivity and sensing time are the key features for spectrum sensing in a cognitive radio (CR) which detects empty bands within VHF/UHF television broadcast bands and uses them as a secondary user. In this paper, an integrated CMOS CR spectrum sensor for a CR receiver in the 54–862 MHz band is presented. A quasi-cyclostationary feature (QCF) detector is proposed based on both energy and feature detection methods and can take advantage of both methods to reach a fast and accurate decision without the need for an analog-to-digital converter for decision making. The integrated chip has been fabricated in a standard $0.18{\mathchar"702D}\mu\hbox {m}$ CMOS IBM technology and has achieved minimum detection signal-to-noise ratio of as low as $-24~\hbox {dB}$ and dynamic range (DR) of 39 dB.

A CMOS Spectrum Sensor Based on Quasi-Cyclostationary Feature Detection for Cognitive Radios

In this study, the design of active-RC filters using opamps with and without feed-forward-compensation is considered. Accurate analysis of the passive compensation scheme suggested in literature for lossless and lossy integrators using feed-forward-compensated opamps is carried out. The compensation for the lossy and lossless integrators using negative impedance converter for active filters using two cascaded gm s in place of opamps is explored. Novel building blocks for realising the negative capacitance needed for exact compensation are proposed. To study the efficacy of the proposed compensation technique, a two-integrator loop biquad is considered. The PSPICE simulation results of Tow-Thomas biquad are presented to highlight the performance improvement obtained using the proposed compensation techniques.

Active-RC filters using two-stage OTAs with and without feed-forward compensation

A 350 MHz fifth-order elliptic opamp-RC filter demonstrates that opamp-based filters need not have bandwidth disadvantages compared to transconductor-based filters The filter, fabricated in standard digital 018 /spl mu/m CMOS with 18 V V/sub DD/, achieves 05 Vp-p signal swing at -40 dB THD

N. Weste

Papers

350 MHz opamp-RC filter in 0.18 m CMOS