A low-distortion active filter is realized using current-efficient feedforward-compensated operational amplifiers in the integrators and feedforward current injection in the summing amplifier. A third-order elliptic low-pass filter with two possible bandwidth settings of 17 and 8.5 MHz consumes 1.8 mW from a 1.8-V supply and occupies 0.17 μm2 in a 0.18- μm CMOS process. The measured maximum signal-to-noise and distortion ratios at the two bandwidth settings are 50.5 and 52.5 dB, respectively. The corresponding third-order intermodulation intercept points (IIP3) are +28.2 and +30.8 dBm. Automatic tuning is used at the startup to counter process variations and set the bandwidth accurately. © 2011 IEEE.

Nagendra Krishnapura

Department of Electrical Engineering

AUTOMATIC TUNING

CMOS processs

CONTINUOUS-TIME FILTERS

Elliptic filters

Feed-Forward

FEED-FORWARD COMPENSATION

FEEDFORWARD CURRENT

INTERCEPT POINTS

LOW-DISTORTION

Process Variation

SIGNAL TO NOISE AND DISTORTION RATIO

Third-order

THIRD-ORDER INTERMODULATION

Bandwidth

CMOS integrated circuits

Continuous time systems

ELECTRIC FILTERS

geometry

Integrated circuits

Low pass filters

Operational amplifiers

Active filters

Fulltext

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IIT Madras

A High-IIP3 Third-Order Elliptic Filter With Current-Efficient Feedforward-Compensated Opamps

IEEE Transactions on Circuits and Systems II: Express Briefs

This paper demonstrates a completely on-chip implementation of expansion and compression of continuous-time, wideband, analog pulses. The input pulse is fed to a continuous-time filter whose delay exceeds the pulse duration. Once the pulse is completely inside the filter, it is stored in the form of the filter's state-variables, which can completely reconstruct the pulse. Instantaneously decreasing or increasing the filter's bandwidth at this instant results in the output pulse being expanded or compressed, respectively, compared with when the bandwidth is unchanged. A 1.6 mm2, 370 mW, 0.13 μ text{m} prototype has a delay filter whose bandwidth can be switched between 870 and 472 MHz. It achieves 1.8\times pulse expansion and 1.7\times pulse compression with an rms error which is 33 dB below the peak-peak pulse amplitude. © 2004-2012 IEEE.

IEEE Transactions on Circuits and Systems I: Regular Papers

Expansion and compression of analog pulses by bandwidth scaling of continuous-time filters

The output common-mode voltage in multistage fully differential opamps can be set by using a single common-mode feedback loop around all stages or by independent loops for each stage. The two schemes are analyzed for their impact on the slew rate in a two-stage Miller-compensated class-A opamp. Analysis and simulation results show that using local common-mode feedback loops will lead to higher slew rate. This is because, when slewing, both upper and lower transistors receive signal dependent gate voltages with local common-mode feedback, making the behavior similar to that of a class-AB output stage. Also, with local common-mode feedback, the positive and negative slew rates are symmetric. © 2015 IEEE.

Proceedings of the IEEE International Conference on VLSI Design

On Slew Rate Enhancement in Class-A Opamps Using Local Common-Mode Feedback

We present techniques for accurately characterizing the frequency response and noise spectral density of integrated continuous-time filters. A 75-MHz fifth-order Chebyshev Gm-C ladder filter designed in a 0.35-μm CMOS process and packaged in a 40-pin DIP is used as a test vehicle to validate the ideas proposed in this work. When compared to conventional frequency response measurement methods, the proposed techniques show a significantly enhanced measurement accuracy in the stopband, while being less sensitive to package characteristics. © 2007 IEEE.

IEEE Journal of Solid-State Circuits

Accurate characterization of integrated continuous-time filters

A high-IIP3 third-order elliptic filter with current-efficient feedforward-compensated opamps

Journal	IEEE Transactions on Circuits and Systems II: Express Briefs
ISSN	15497747
Open Access	Yes