Linear Operational Transconductance Amplifier Research Articles

HIGH-FREQUENCY LINEAR MULTIPLE-OUTPUT CMOS TRANSCONDUCTANCE AMPLIFIER FOR CURRENT-MODE FILTERS

A high-frequency highly linear tunable CMOS multiple-output operational transconductance amplifier (MO-OTA) for fully balanced current-mode OTA and capacitor (OTA-C) filters is presented. The MO-OTA is based on the cross-coupled pairs at the input and provides two pairs of differential outputs. A simple common-mode feedback (CMFB) circuit to stabilize the DC output levels of the MO-OTA is also proposed and two such CMFB circuits are used by the MO-OTA. The proposed MO-OTA is suitable for relatively low voltage (2.5 V) applications as its circuit has only two MOS transistors between the supply and ground rails. Simulated in a TSMC 0.25 μm CMOS process using PSpice, the MO-OTA has at least ± 0.3 V linear differential input signal swing with a single 2.5 V power supply and operates up to 1 GHz frequency. The MO-OTA has a THD less than -46 dB for a differential input voltage of 0.9 Vp-p at 10 MHz, dynamic range (DR) at THD = -46 dB is over 50 dB, and power consumption (with the common-mode feedback circuit) is below 8 mW for the whole tuning range. A fully balanced multiple loop feedback current-mode OTA-C filter example using the proposed MO-OTA is presented. This example also shows that the current-mode follow-the-leader-feedback (FLF) structure can achieve good performances for OTA-C filter design.

A High-Frequency Transconductor Using a Robust Nonlinearity Cancellation

This brief deals with the design of a linear operational transconductance amplifier (OTA) intended for high-frequency continuous-time filters. Three source-degenerated differential pairs are used to reduce the third-order distortion components regardless of process parameter tolerances and bias current. Experimental results for an OTA fabricated in the TSMC 0.35-mum CMOS process are presented and compared with recently reported topologies. Draining 2.8 mA from a single supply voltage of 3.3 V, the transconductor achieves IM3<-70 dB for a two-tone input signal of 1.3 Vpp measured at 70 MHz. The input referred noise density is only 7 nV/radicHz, leading to an SNR of 75 dB

1.33 mW, 2 V CMOS continuous-time bandpass filter with two decades of centre frequency tuning range and high Q

A gm-C bandpass biquad filter featuring two decades of centre frequency tuning capability and a wide range of quality factor tunability is presented. It uses a new linear operational transconductance amplifier (OTA) based on two crosscoupled class-AB pseudo-differential pairs, which exhibits a wide transconductance adjustability range with low power consumption. The filter has been fabricated in a standard 0.8 μm CMOS process. Experimental results show a frequency tuning range from 300 kHz to 32 MHz and a maximum quality factor of 501. The filter is operated at 2 V supply voltage with a power consumption ranging from 1.18 to 1.8 mW.

A novel CMOS operational transconductance amplifier based on a mobility compensation technique

This brief describes a new linear operational transconductance amplifier (OTA) and its application to a ninth-order Bessel filter. To improve the linearity of the OTA, we employ a mobility compensation circuit which combines the transistors operating in the triode and the subthreshold regions. The proposed technique enhances the linearity of the transconductance without loss of the input swing range. The proposed OTA shows /spl plusmn/0.5% Gm variation and the total harmonic distortion of less than - 60-dB over the input range of /spl plusmn/0.8-V. The ninth-order Bessel filter employing the proposed OTA has been implemented in a 0.35-/spl mu/m n-well CMOS process under 3.3-V supply voltage. It shows the cutoff frequency of 8 MHz and the power consumption of 65 mW.

A Monolithic Positioning System

A monolithic positioning system operating with absolute coded magnetic scales is presented. The system is intended for precise absolute positioning in industrial applications. Mounted on a tool, the sensor system moves along a stationary scale. A sophisticated comb of sensors reads out the magnetic coding allowing the absolute position to be calculated. The main task has been to cancel the immense sensor offsets. Numerous structures have been measured in order to get statistically assured data of sensitivity and offset variation. A sensor readout technique without large offset cancellation circuitry is discussed. Furthermore a novel linear operational transconductance amplifier (OTA) is shown.

A 60-mW 200-MHz continuous-time seventh-order linear phase filter with on-chip automatic tuning system

A full CMOS seventh-order linear phase filter based on g/sub m/-C biquads with a -3-dB frequency of 200 MHz is realized in 0.35-/spl mu/m CMOS process. The linear operational transconductance amplifier is based on complementary differential pairs in order to achieve both low-distortion figures and high-frequency operation. The common-mode feedback (CMFB) employed takes advantage of the filter architecture; incorporating the load capacitors into the CMFB loop improves further its phase margin. A very simple automatic tuning system corrects the filter deviations due to process parameter tolerances and temperature variations. The group delay ripple is less than 5% for frequencies up to 300 MHz, while the power consumption is 60 mW. The third-harmonic distortion is less than -44 dB for input signals up to 500 mV/sub pp/. The filter active area is only 900 /spl times/ 200 /spl mu/m/sup 2/. The supply voltages used are /spl plusmn/1.5 V.

Full CMOS continuous time filters for GSM applications

This paper describes full cmoscontinuous time filter design techniques which can meet the specifications commonly set for gsmapplications. First several cmosfilter design techniques are overviewed. The ota-ctechnique is discussed to some more detail. To overcome the main drawback of the lower total harmonic distortion in ota-ctechniques very linear operational transconductance amplifiers (ota)are required. Such an ota,together with the applied linearisation techniques is discussed. To fulfil high accuracy in cut- off frequencies of the filter an active tuning system is necessary. A new on- chip tuning system is presented. The paper concludes with a practical design example for the gsmsystem. Therein the different ota-ctechniques discussed are illustrated.

Design of a 2.7-GHz linear OTA and a 250-MHz elliptic filter in bipolar transistor-array technology

The design of a tunable high-frequency fully differential bipolar operational transconductance amplifier (OTA) is presented. Techniques resulting in tunability and broadbanding are discussed, as are unavoidable tradeoffs resulting from the lack of a vertical pnp device. Using an 8-GHz bipolar transistor array process, the simulated -3-dB frequency of the OTA is over 2.7 GHz, the maximum linear input range is +or-2.5 V, and the power dissipation is 28 mW for a power supply of +or-5 V. The OTA can also operate at a +or-2.5 V. The design of a third-order elliptic OTA-C filter with cutoff frequency of 250 MHz and tuning range from 200 to 290 MHz is presented. Filter nonidealities are analyzed, and predistortion and compensation techniques, are discussed. Temperature variations from -30 to +100 degrees C and supply variations from +or-4.5 to +or-7.5 V change the cutoff frequency of the filter by less than 10%. The Q-factor can be electronically adjusted for all frequencies in the tuning range. >

A linear operational transconductance amplifier for instrumentation applications

A linear operational transconductance amplifier (OTA) is described that consists of a linear transconductor and a translinear current gain cell followed by three current mirrors. The proposed circuit has superior linearity and temperature characteristic when compared with the commercially available OTA. A prototype circuit with a transconductance of 50 mu S has been built with discrete bipolar transistors producing a linearity error of less than +or-20% over an input voltage range from -0.8 to 0.8 V. The prototype OTA circuit also exhibits a transconductance that is linearly dependent on a bias current varying over four decades with a sensitivity of 1 S/A.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-voltage BICMOS and vertical OTA

A linear BICMOS operational transconductance amplifier (OTA) with low voltage supply requirements is presented. Two versions of this circuit using stacked and folded BICMOS composite transistors are discussed. Simulations and experimental results using transistor arrays are shown that verify the operating principle of the proposed structures.