Low‐Voltage Tunable Pseudo‐Differential Transconductor with High Linearity

A novel tunable transconductor is presented. Input transistors operate in the triode region to achieve programmable voltage‐to‐current conversion. These transistors are kept in the triode region by a novel negative feedback loop which features simplicity, low voltage requirements, and high output resistance. A linearity analysis is carried out which demonstrates how the proposed transconductance tuning scheme leads to high linearity in a wide transconductance range. Measurement results for a 0.5 μm CMOS implementation of the transconductor show a transconductance tuning range of more than a decade (15 μA/V to 165 μA/V) and a total harmonic distortion of ?67 dB at 1 MHz for an input of 1 V_pp and a supply voltage of 1.8 V.     

Multimode $G_{m}$– $C$ Channel Selection Filter for Mobile Applications in 1-V Supply Voltage

A CMOS transconductor for multimode channel selection filter is presented. The transconductor includes a voltage-to-current converter and a current multiplier. Voltage-to-current conversion employs linear region MOS transistors, and the conversion features high linearity over a wide input swing range. The current multiplier which operates in the weak inversion region provides a wide transconductance tuning range without degrading the linearity. A third-order Butterworth low-pass filter implemented with the transconductors was designed by TSMC 0.18 mum CMOS process. The measurement results show that the filter can operate with the cutoff frequency of 135 kHz to 2.2 MHz. The tuning range and the linearity performance would be suitable for the wireless specifications of GSM, Bluetooth, cdma2000, and wide-band CDMA. In the design, the maximum power consumption at the highest cutoff frequency is 2 mW under a 1-V supply voltage.     

Low-voltage pseudo-differential transconductor with improved tunability-linearity trade-off

A new low-voltage pseudo-differential CMOS transconductor using transistors in the saturation region is presented. It keeps the input common-mode voltage constant, while its transconductance is easily tunable through a DC voltage preserving linearity for a moderate range of G/sub m/ values. Post-layout results for a 2.7 V-0.5 /spl mu/m CMOS design dissipating less than 1.5 mW show a 1:2 G/sub m/ tuning range with an almost constant bandwidth over 600 MHz. Total harmonic distortion figures are below -60 dB over the whole range at 10 MHz up to a 100 /spl mu/A/sub p-p/ differential output.     

An active device based wide tuning range CMOS transconductor

A CMOS transconductor for wide tuning range filter application is presented. The linear transconductor is designed based on the flipped-voltage follower (FVF) circuit and can work in the weak, moderate, and strong inversion regions to maximize the transconductance tuning range. The transconductance tuning can be achieved by changing the bias current of the active resistor, and a ratio of 28 is obtained. The transconductor was evaluated by using TSMC 0.18 μm CMOS process, and the total harmonic distortion (THD) of −56 dB can be obtained by giving a 12 MHz 0.4 Vpp input swing signal. In the design, the maximum power consumption is 2 mW with the transconductance of 1.1 mS under a 1.8 V supply voltage.     

Highly Linear Tunable CMOS $Gm{hbox{-}}C$ Low-Pass Filter

A comprehensive analysis of tunable transconductor topologies based on passive resistors is presented. Based on this analysis, a new CMOS transconductor is designed, which features high linearity, simplicity, and robustness against geometric and parametric mismatches. A novel tuning technique using just a MOS transistor in the triode region allows the adjustment of the transconductance in a wide range without affecting the voltage-to-current conversion core. Measurement results of the transconductor fabricated in a 0.5- mum CMOS technology confirm the high linearity predicted. As an application, a third-order Gm-C tunable low-pass filter fabricated in the same technology is presented. The measured third-order intermodulation distortion of the filter for a single 5-V supply and a 2-V_pp two-tone input signal centered at 10 MHz is -78 dB.     

A low-power low-voltage OTA-C sinusoidal oscillator with a large tuning range

A new operational transconductance amplifier and capacitor based sinusoidal voltage controlled oscillator is presented. The transconductor uses two cross-coupled class-AB pseudo-differential pairs biased by a flipped voltage follower, and it exhibits a wide transconductance range with low power consumption and high linearity. The oscillator has been fabricated in a standard 0.8-/spl mu/m CMOS process. Experimental results show a frequency tuning range from 1 to 25 MHz. The amplitude is controlled by the transconductor nonlinear characteristic. The circuit is operated at 2-V supply voltage with only 1.58 mW of maximum quiescent power consumption.     

Low-Voltage Linearly Tunable CMOS Transconductor With Common-Mode Feedforward

This paper presents a new low-voltage pseudodifferential continuous-time CMOS transconductor for wide-band applications. The proposed cell is based on a feedforward cancellation of the input common-mode signal and keeps the input common mode voltage constant, while the transconductance is easily tunable through a continuous bias voltage. Linearity is preserved during the tuning process for a moderate range of transconductance values. Measurements results for a 0.35-m CMOS design show a 1:2 tuning range with total harmonic distortion figures at 10 MHz below 58 dB over the whole range up to a 200- differential output current. The proposed cell consumes less than 1.1 mW from a single 1.8-V supply.     

A Wide Tuning Range Gm –C Continuous-Time Analog Filter

A CMOS operational transconductance amplifier (OTA) for low-power and wide tuning range filter application is proposed in this paper. The OTA can work from the weak inversion region to the strong inversion region to maximize the transconductance tuning range. The transconductance can be tuned by changing its bias current. A fifth-order Elliptic low-pass filter implemented with the OTAs was integrated by TSMC 0.18-mum CMOS process. The filter can operate with the cutoff frequency of 250 Hz to 1 MHz. The wide tuning range filter would be suitable for multi-mode applications, especially under the consideration of saving chip areas. The third-order inter-modulation (IM3) of -40 dB was measured over the tuning range with two tone input signals. The power consumption is 0.8 mW at 1-MHz cutoff frequency and 1.8-V supply voltage with the active area less than 0.3 mm²     

A linear compact tunable transconductor for Gm-C applications

A CMOS highly linear voltage-controlled transconductor suitable for Gm-C filter design is presented. The control loop to program the transconductance maintains the input transistors in triode region with a compact topology. Measurement results for the transconductor fabricated in a 0.5-??m CMOS technology feature a spurious-free dynamic range (SFDR) of 72?dB for 1 V_pp differential inputs at 1?MHz. The voltage to current converter ensures a high linearity level for a wide transconductance range. Functionality of the transconductor is shown in a fifth-order Gm-C tunable complex filter well suited for a dual-mode Bluetooth/Zigbee transceiver.     

A Tunable Pseudo-Differential OTA With $-78~{hbox {dB}}$ THD Consuming 1.25 mW

A novel linear tunable transconductor based on a combination of linearization techniques is presented. The input signal is transferred to the V-I conversion element by means of a high-speed feedback loop. Then, the linear V-I conversion is accomplished using quasi-floating-gate MOS transistors biased in the triode region. Finally, the absence of current mirrors in the signal path provides low sensitivity to transistor mismatch and reduces the harmonic distortion. The operational transconductance amplifier (OTA) was fabricated in a 0.5-mum CMOS technology with a single 3.3-V supply voltage. Experimental results show a total harmonic distortion of -78 dB at 1 MHz with 1-V_pp input signal. High linearity of the OTA is obtained over a two octave tuning range with only 1.25-mW power consumption.     

应用于跨导放大器设计的线性度优化方法

 基于跨导放大器线性度理论和数学分析,提出了一种提高线性度的方法.该方法通过数学理论分析和模拟实验证实,双端输入双端输出结构的跨导器线性度优于单端输入单端输出的跨导器,且两个输入端信号满足一端是另一端幅度的4/3倍加1时,跨导器线性失真度最小.根据该优化方法设计了一种新型跨导器,仿真实验表明,跨导器无杂散动态范围为60.25dB,噪声平台达到-100dB.     

Low-voltage CMOS triode transconductor with wide-range and lineartunability

A triode transconductor is proposed which has a transconductance that is linearly tuneable over a wide range (more than two decades) when the circuit is operated from a 3.3 V power supply. The THD is <1% within the whole linear tuning range, for a 10 MHz differential input signal of 1 V_peak     

Highly linear programmable balanced current scaling technique in moderate inversion

A technique to achieve highly linear current scaling in CMOS technologies is proposed. It is based on two balanced electronically programmable current mirrors operating in moderate inversion. The scaling factor can be continuously adjusted in a wide range. This technique can be employed to achieve or to extend gain adjustment in amplifiers. As an application example, a variable-gain differential current amplifier and a tunable transconductor are presented. Measurement results of the transconductor implemented in a 0.5-/spl mu/m CMOS technology validate in silicon the proposed approach.     

A CMOS “soft-switched” transconductor and itsapplication in gain control and filters

This paper presents a transconductor suitable for implementation in submicron CMOS technology. The transconductor is nearly insensitive for the second-order effects of the MOS transistors, which become more and more prevalent in today's submicron processes. The transconductor relies on a differential pair with variable degeneration resistance, while the degeneration resistors are “soft-switched” by means of MOS transistors. The transconductance is continuously tunable. A transconductor, using a device in which the degeneration resistors and “soft switches” are merged, is optimized for a maximum tuning range and can be used in variable gain stages like in an automatic gain control (AGC) circuit. Besides, a third-order 5.5 MHz low-pass filter has been realized in a 0.5-μm CMOS process using the “soft-switched” transconductor. At a 3.3 V supply voltage the filter dissipates 12 mW and the dynamic range equals 62 dB where the total harmonic distortion (THD) is -48 dB for an input voltage of 1 Vpp     

A low-voltage, highly linear voltage-controlled transconductor

A low-voltage fully differential, voltage-controlled transconductor is described. The proposed transconductor achieves a wide input/control voltage range, with a highly linear transconductance factor and truly fully differential output currents. The transconductor is used to implement a G/sub m/-C adaptive forward equalizer (FE) for a 125 Mbps wire line transceiver using digital core transistors with channel length of no more than double the feature size in a typical digital CMOS 180-nm process and supply voltage as low as 1.6 V. The adaptive FE enables IEEE 1394b transceivers to operate over UTP-5 cables for up to 100 m in length. The transconductor stage occupies 1945 /spl mu/m/sup 2/ and consumes an average power of 418 /spl mu/w at 125 Mbps and 1.8-V supply.     

Sub 1-V highly-linear low-power class-AB bulk-driven tunable CMOS transconductor

This paper describes the design and realization of a sub 1-V low power class-AB bulk-driven tunable linear transconductor using a 0.18-μm CMOS technology. The proposed transconductor employs a class-AB bulk-driven differential input voltage follower and a passive resistor to achieve highly linear voltage-to-current conversion. Transconductance tuning is achieved by tuning the differential output current of the core transconductor with gain-adjustable current mirrors. With 10.4-μA current consumption from a 0.8-V single power supply voltage, simulation results show that the proposed transconductor achieves the total harmonic distortion (THD) of <?40 dB for a peak differential input voltage range of 800 mV at frequencies up to 10 kHz. The simulated input-referred noise voltage integrated over 10-kHz bandwidth is 100 μV, resulting to an input signal dynamic range of 75 dB for THD <?40 dB. A biquadratic G_m-C filter is designed to demonstrated the performance of the proposed transconductor. At the nominal 10-kHz cut-off frequency, the filter dissipates 34.4 μW from a 0.8-V supply voltage and it achieves an input signal dynamic range of 67.4 dB for the third-order intermodulation distortion of <?40 dB.     

OTA linearity enhancement technique for high frequency applications with IM3 below -65 dB

A technique to enhance the linearity of continuous-time operational transconductance amplifiers (OTA)-C filters working at high frequencies is proposed. Each OTA consumes 10.5 mW and the transconductance can be tuned from 70 to 160 /spl mu/A/V while the IM3 remains below -70 dB up to 50 MHz for a 1.3-V/sub pp/ differential input. For a 20-MHz low-pass second-order filter implementation, the measured IM3 with an input voltage of 1.3 V/sub pp/ is below - 65 dB. The supply voltage is 3.3 V. Experimental results of the circuit, fabricated in a standard CMOS 0.35-/spl mu/m technology, are presented.     

Tunable operational transconductance amplifier with extremely high linearity over very large input range

A simply fully-differential transconductor is presented that achieves, based on cancellation of first and higher order nonlinearities, +or-0.7% linearity error over a +or-6.4 V differential input range for +or-5 V power supplies. Common-mode input signals are cancelled at the output. The transconductance can be tuned at least by a factor 3 and f/sub (-3dB)/ is 63 MHz for 10 mu m channel length.<>     

A CMOS transconductor with 80-dB SFDR up to 10 MHz

A CMOS transconductor uses resistors at the input and an OTA in unity-gain feedback to achieve 80-dB spurious-free dynamic range (SFDR) for 3.6-V_pp differential inputs up to 10 MHz. The combination of resistors at the input and negative feedback around the operational transconductance amplifier (OTA) allows this transconductor to accommodate a differential input swing of 4 V with a 3.3-V supply. The total harmonic distortion (THD) of the transconductor is -77 dB at 10 MHz for a 3.6-V_pp differential input and third-order intermodulation spurs measure less than -79 dBe for 1.8-V_pp differential inputs at 1 MHz. The transconductance core dissipates 10.56 mW from a 3.3-V supply and occupies 0.4 mm² in a 0.35-μm CMOS process     

A Fully Integrated Single-Ended 1.5–15-Hz Low-Pass Filter With Linear Tuning Law

A second-order, single-ended, fully integrated low- pass filter with cut-off frequency tunable in the range 1.5-15 Hz is presented. The filter is based on a recently proposed CMOS transconductor topology, combining G_m values of the order of a few nS with large input ranges and suitability to single-ended filter architectures. The circuit has been designed and fabricated using 3.3-V 0.35-mum CMOS devices from the STMicroelectronics Bipolar-CMOS-DMOS process BCD6. The tested prototype occupies an area of 960 x 350 mum² and requires a supply current ranging from 50 to 500 muLambda, depending on tuning. Total harmonic distortion lower than 1% has been measured in a wide tuning range for 1-V peak-to-peak input signal amplitude. The effect of temperature on the tuning law in the interval 0-80degC is shown. A dynamic range in excess of 60 dB over the whole tuning range has been estimated from distortion and noise measurements.