CMOS circuits for integrated analog filters at very high frequencies, based on transconductance-C integrators, are presented. First a differential transconductance element based on CMOS inverters is described. With this circuit a linear, tunable integrator for very-high-frequency integrated filters can be made. This integrator has good linearity properties and nondominant poles in the gigahertz range owing to the absence of internal nodes. The integrator has a tunable DC gain, resulting in a controllable integrator quality factor. Experimental results of a VHF CMOS transconductance-C low-pass filter realized in a 3- mu m CMOS process are given. Both the cutoff frequency and the quality factors can be tuned. The cutoff frequency was tuned from 22 to 98 MHz and the measured filter response is very close to the ideal response of the passive prototype filter. Furthermore, a novel circuit for automatically tuning the quality factors of integrated filters built with these transconductors is described. >

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A CMOS transconductance-C filter technique for very high frequencies

The linear range of approximately ±75 mV of traditional subthreshold transconductance amplifiers is too small for certain applications—for example, for filters in electronic cochleas, where it is desirable to handle loud sounds without distortion and to have a large dynamic range. We describe a transconductance amplifier designed for low-power (< 1 µW) subthreshold operation with a wide input linear range. We obtain wide linear range by widening the tanh, or decreasing the ratio of transconductance to bias current, by a combination of four techniques. First, the well terminals of the input differential-pair transistors are used as the amplifier inputs. Then, feedback techniques known as source degeneration (a common technique) and gate degeneration (a new technique) provide further improvements. Finally, a novel bump-linearization technique extends the linear range even further. We present signal-flow diagrams for speedy analysis of such circuit techniques. Our transconductance reduction is achieved in a compact 13-transistor circuit without degrading other characteristics such as dc-input operating range. In a standard 2 µm process, we were able to obtain a linear range of ±1.7V. Using our wide-linear-range amplifier and a capacitor, we construct a follower–integrator with an experimental dynamic range of 65 dB. We show that, if the amplifier‘s noise is predominantly thermal, then an increase in its linear range increases the follower–integrator‘s dynamic range. If the amplifier‘s noise is predominantly 1/f, then an increase in its linear range has no effect on the follower–integrator‘s dynamic range. To preserve follower–integrator bandwidth, power consumption increases proportionately with an increase in the amplifier‘s linear range. We also present data for changes in the subthreshold exponential parameter with current level and with gate-to-bulk voltage that should be of interest to all low-power designers. We have described the use of our amplifier in a silicon cochlea [1, 2].

A Low-Power Wide-Linear-Range Transconductance Amplifier

A 12th-order OTA-C complex filter with a nonconventional frequency tuning for a Bluetooth receiver is implemented in a low-cost mainstream 0.35-/spl mu/m CMOS process. This proposed frequency tuning scheme is simpler than the conventional one based on phased-locked loop (PLL). Furthermore, a high-speed pseudo differential OTA using common-mode feedforward (CMFF) and common-mode feedback (CMFB) strategy is proposed. The filter bandwidth is 1 MHz and is centered at 2 MHz. Image and adjacent channels are attenuated by more than 45 and 27 dB, respectively. The integrated input referred noise is 29 /spl mu/V/sub rms/, and the filter chip dissipates 4.7 mA from a 2.7 V supply. The theoretical and experimental results are in good agreement.

A pseudo differential complex filter for Bluetooth with frequency tuning

A method to design integratable continuous-time analog high-Q bandpass filters with a prescribed dynamic range is developed. The theory accompanying this method shows the fundamental restrictions for the dynamic range. The theory is meant to determine beforehand if the desired dynamic range is realizable. The possibilities of using dynamic range optimal filter networks are discussed. The usefulness of the theories is shown by the design of a complete bandpass filter, up to the transistor level. >

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The design of high dynamic range continuous-time integratable bandpass filters

Covering the essentials of analog circuit design, this book takes a unique design approach based on a MOSFET model valid for all operating regions, rather than the standard square-law model. Opening chapters focus on device modeling, integrated circuit technology, and layout, whilst later chapters go on to cover noise and mismatch, and analysis and design of the basic building blocks of analog circuits, such as current mirrors, voltage references, voltage amplifiers, and operational amplifiers. An introduction to continuous-time filters is also provided, as are the basic principles of sampled-data circuits, especially switched-capacitor circuits. The final chapter then reviews MOSFET models and describes techniques to extract design parameters. With numerous design examples and exercises also included, this is ideal for students taking analog CMOS design courses and also for circuit designers who need to shorten the design cycle.

http://www.gbv.de/dms/ilmenau/toc/621660655.PDF

CMOS Analog Design Using All-Region MOSFET Modeling

A differential transconductance element based on CMOS inverters is presented. With this circuit a linear, tunable integrator for very high-frequency continuous-time integrated filters can be made. This integrator has good linearity properties (THD<0.04%, Vipp=1.8 V), nondominant poles in the gigahertz range and a 40 dB DC gain

/pdf/linear-cmos-transconductance-element-for-vhf-filters-45bn0jfbxo.pdf

Linear CMOS transconductance element for VHF filters

In this paper a CMOS temperature-to-current converter is presented of which the output current is the difference between a PTC current and an NTC current. The PTC current is derived from a PTAT cell, while the NTC current is derived from a threshold voltage reference source. It is shown that this way of current subtraction diminishes to a certain extent the effects of the thermal dependence of the resistors used.

/pdf/design-of-a-cmos-temperature-sensor-with-current-output-48wi1lckus.pdf

Design of a CMOS temperature sensor with current output

A CMOS third order elliptic low-pass filter with a 110MHz cut-off frequency realized in a 3?m-process is presented. The filter consists of differential transconductance elements and capacitors. The transconductance element has good linearity properties and an excellent high frequency behaviour thanks to the absence ofinternal nodes. Both the cut-off frequency and the Q-factors can be tuned.

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A 110MHz CMOS Transconductance-C Low-Pass Filter

https://ris.utwente.nl/ws/files/6561188/Kolling89two.pdf

Evert Seevinck

Papers

Linear CMOS transconductance element for VHF filters

Design of a CMOS temperature sensor with current output

A 110MHz CMOS Transconductance-C Low-Pass Filter

Two-lead multiplex system for sensor array applications