Continuous-time Common-mode Feedback Research Articles

Compact Continuous Time Common-Mode Feedback Circuit for Low-Power, Area-Constrained Neural Recording Amplifiers

A continuous-time common-mode feedback (CMFB) circuit for low-power, area-constrained neural recording amplifiers is proposed. The proposed CMFB circuit is compact; it can be realized by simply replacing passive components with transistors in a low-noise folded cascode operational transconductance amplifier (FC-OTA) that is one of the most widely adopted OTAs for neural recording amplifiers. The proposed CMFB also consumes no additional power, i.e., no separate CMFB amplifier is required, thus, it fits well to low-power, area-constrained multichannel neural recording amplifiers. The proposed CMFB is analyzed in the implementation of a fully differential AC-coupled neural recording amplifier and compared with that of an identical neural recording amplifier using a conventional differential difference amplifier-based CMFB in 0.18 μm CMOS technology post-layout simulations. The AC-coupled neural recording amplifier with the proposed CMFB occupies ~37% less area and consumes ~11% smaller power, providing 2.67× larger output common mode (CM) range without CM bandwidth sacrifice in the comparison.

Switched-Capacitor Common-Mode Feedback-Based Fully Differential Operational Amplifiers and its Usage in Implementation of Integrators

For stabilizing the common-mode output voltage of fully differential operational amplifiers, switched-capacitor (SC) type of common-mode feedback (CMFB) is a familiar technique. This is appropriate for implementing high-gain wide-swing low-power op-amps due to its benefits of minimum power consumption, superior linearity across a large amplifier output swing range, and improved feedback loop stability in comparison to continuous-time CMFB. However, the usage of SC-CMFB requires careful attention to some realistic aspects, details of many of which are available in literature. Nonetheless, its adverse effect on the op-amp’s differential-mode gain has not been investigated much. The explanation for this effect is the SC-CMFB-induced equivalent resistive loading, and this is particularly significant in amplifiers like folded cascode which are intended to provide a high gain. This issue of drop in op-amp dc gain because of SC-CMFB, and the consequence on the realization of continuous-time and discrete-time forms of integrators utilizing such amplifiers is the topic of discussion in this paper. Relevant analytical derivations and circuit simulations at the transistor level are provided. A couple of design guidelines and circuit topologies for minimizing the loading-induced gain reduction are also presented.

Class AB differential difference amplifier for enhanced common‐mode feedback

A class AB differential difference amplifier for continuous-time common-mode feedback (CMFB) is presented. It employs local CMFB to improve gain-bandwidth product and dynamic performance of the CMFB loop, without increasing static power consumption or supply voltage requirements. Measurement results for a 0.5 μm CMOS test chip prototype validate the proposal.

In brief

PAGE 459 A Schmitt trigger circuit which uses one multiple output current follower differential input transconductance amplifier (MO-CFDITA), and one grounded resistor is presented in this Letter. The circuit simultaneously provides clockwise and anticlockwise hysteresis, which are independently and electronically controllable. This research from India has applications in electric motor devices and dc-dc converters. PAGE 450 A low cost real-time model for mean arterial pressure (MAP) has been developed by researchers in Brazil. The model simulates the response of patients to the drug sodium nitroprusside (SNP). Compared with real patient data for a targeted MAP of 100 mmHg, the model gave an error of less than 3%. Schmitt trigger circuit using a single MO-CFDITA and grounded resistor. PAGE 487 A high-frequency waveguide bandpass filter based on TM120 resonators is proposed. TM120 resonators are nearly twice as large as conventional TE101 resonators and have a reduced aspect ratio, making the computer numerical control (CNC) milling process easier. The technology, a result of collaboration between researchers from the UK and China, can be applied to terahertz waveguide filters. Low cost, real-time mean arterial pressure model to simulate response to drug SNP. PAGE 454 A local common-mode feedback scheme for differential difference amplifiers is presented. This scheme improves the speed and accuracy of continuous-time common-mode feedback (CMFB) circuits without the need for extra power or supply voltage. Researchers from Spain and China used a 0.5 µm CMOS chip prototype to test the technology. W-band filter based on TM120 resonators. PAGE 493 Researchers from China have used a digital Wiener filter to enable PAM-4 single lane 100 Gb/s over 4-km and 320 Gb/s (4×80 Gb/s) over 8-km standard single-mode fibre (SSF). The work demonstrates the potential application of alternative digital signal processing methods to enable high-speed links in short reach optical interconnect. Improved accuracy and speed without extra power for CMFB circuits. Weiner filters used in short reach optical interconnect.

Common Mode Feedback Circuits for Low Voltage Fully-Differential Amplifiers

Continuous time common mode feedback (CMFB) circuits for low voltage, low power applications are proposed. Four circuits are proposed for gate/bulk-driven pseudo-differential transconductors operating on sub-1-V power supply. The circuits are validated for a bulk-driven pseudo-differential transconductor operating on 0.5[Formula: see text]V in 0.18[Formula: see text][Formula: see text]m standard CMOS technology. Simulation results reveal that the proposed CMFB circuits offer power efficient solution for setting the output common mode of the transconductors. They also load the transconductor capacitively offering capacitance of about 1[Formula: see text]fF to tens of femto farads.

An Ultra High speed Low power Low settling time error and wide dynamic range voltage Continuous-time Common-Mode Feedback Circuit in 0.18µm CMOS

A novel method to design continuous-time common-mode feedback circuit is presented in this paper. The main purposes of the proposed idea are increasing the speed and decreasing the settling time error of the common-mode feedback circuit, besides it has a wide dynamic rang voltage to set the output in desired value as well. As MATLAB simulation result shows the proposed circuit can adjust the output in reliable value by applying the reference voltage (Vref) from 0.7 to 1.3 volt very well. Also, the mentioned structure is a proper choice for low voltage application too. The power consumption of the proposed common-mode feedback circuit is just 200µW with power supply of 1.8 volts, and 0.5pF capacitor load is applied at the output nodes of the amplifier. Meanwhile, the proposed circuit is simulated in whole process corner too. Simulation results are performed using the BSIM3 model of a 0.18µm CMOS technology and MATLAB software.

A FAST AND LOW SETTLING ERROR CONTINUOUS-TIME COMMON-MODE FEEDBACK CIRCUIT BASED ON DIFFERENTIAL DIFFERENCE AMPLIFIER

A high-speed and high-accuracy continuous-time common-mode feedback block (CMFB) is presented. To satisfy speed and accuracy requirements, some modifications have been applied on differential difference amplifier (DDA) CMFB circuit. The proposed method is applied to a folded cascode op-amp with power supply of 3.3 V. In order to verify the proposed circuit, simulations are done in 0.35 μm standard CMOS technology. In the worst condition when the output common-mode (CM) voltage is initialized to VCC or GND, only 1.1 ns is required to set the output CM voltage on the desired level. Also in a wide range of input CM voltage variations, the deviation of the output CM voltage from reference voltage is less than 6 mV, so simulation results confirm the expected accuracy and speed while simultaneously the proposed CMFB circuit preserves other characteristics of DDA CMFB circuit such as unity gain frequency, 3-dB bandwidth, phase margin and linearity.

A Family of Low-Voltage Bulk-Driven CMOS Continuous-Time CMFB Circuits

This brief introduces four different structures for implementing a continuous-time common-mode feedback (CMFB) network for fully differential (FD) amplifiers. The proposed circuits use bulk-driven MOS transistors, thus representing a low-voltage realization of their gate-driven counterparts. The CMFB circuits were included in a 1.5-V FD buffer implemented in standard 0.35-μm CMOS technology. Experimental results illustrate the performance of the proposed schemes, demonstrating their suitability to operate with a low supply voltage.

DTMOS Technique for Low-Voltage Analog Circuits

In this paper, the application of dynamic threshold MOS (DTMOS) technique for low-voltage analog circuits is explored. The body terminal of PMOS transistors in bulk CMOS technology can be used as the forth terminal to enhance the performance of low-voltage analog circuits. To show the effectiveness of this technique, we have designed a continuous time common mode feedback (CMFB) circuit for a sub 1-V opamp and a new sub 1-V, 1-bit quantizer. A 0.8-V opamp with embedded CMFB and a 0.8-V, 1-bit quantizer for low-voltage DeltaSigma modulators are implemented in 0.18-mum CMOS technology. The simulation results as well as the measurement data of these blocks are presented in this paper

Continuous-time common-mode feedback for high-speed switched-capacitor networks

This paper deals with the design of a continuous-time common-mode feedback (CMFB) for switched-capacitor networks. Its reduced input capacitance decreases the capacitive load at the output of the fully differential amplifier, improving its achievable gain-bandwidth (GBW) product and slew rate. This topology is more suitable for high-speed switched-capacitor applications when compared to a conventional switched-capacitor CMFB, enabling operation at higher clock frequencies. Additionally, it provides a superior rejection to the negative power supply noise (PSRR/sup -/). The performance of the CMFB is demonstrated in the implementation of a second-order 10.7-MHz bandpass switched-capacitor filter and compared with that of an identical filter using the conventional switched-capacitor CMFB (SC-CMFB). The filter using the continuous-time CMFB reduces the error due to finite GBW and slew rate to less than 1% for clock frequencies up to 72 MHz while providing a dynamic range of 59 dB and a PSRR/sup -/>22 dB. Both circuits were fabricated in 0.35-/spl mu/m CMOS technology.

Continuous time common mode feedback technique for sub 1 V analogue circuits

A continuous time common mode feedback technique for sub 1 V analogue circuits using the bulk PMOS dynamic threshold (BP-DTMOS) technique is presented. The proposed method is used in a 0.8 V folded cascode amplifier in 0.18 µm CMOS technology. The schematic and the post-layout simulation results show that this technique is effective in reducing common mode errors caused by process or environmental variations. It also improves the CMRR of the amplifier.

A continuous-time common-mode feedback circuit (CMFB) for high-impedance current-mode applications

A continuous-time common-mode feedback circuit (CMFB) is presented. A two-stage high-gain architecture is used to stabilize and minimize the offset of the common-mode voltage. A long-channel differential-difference amplifier (DDA) input stage enables this CMFB circuit to have a wide input voltage range without a serious linearity problem. A special compensation scheme enables this circuit to be used in high-impedance current-mode systems without a stability problem. This circuit has been implemented within a continuous-time switched-current /spl Sigma//spl Delta/ modulator in a 2 /spl mu/m CMOS process. It achieves a /spl plusmn/1 V input voltage range with an active area of 100 /spl mu/m/spl times/60 /spl mu/m and a power dissipation of 270 /spl mu/W from a single 5 V power supply.

A low-output-impedance fully differential op amp with large output swing and continuous-time common-mode feedback

A fully differential (zero common-mode voltage) op amp has been developed which has low output impedance, but unlike source-follower output stages, it has a large output swing, namely, 8 V/sub p-p/ for 1-k Omega load and a 5-V supply. The output stage, which is a combination of common-source and source-follower stages, is driven by the two complimentary outputs of the differential-output input stage. A continuous-time common-mode feedback circuit has been used, which due to the op amp's low output impedance, causes negligible open-loop gain (95 dB) degradation. Floating compensation capacitors are used in order to reduce the capacitance value and, hence, the area (490 mil/sup 2/). >

Low-distortion switched-capacitor filter design techniques

The distortion mechanism in switched-capacitor (SC) filters are considered, and closed-form expression relating switched-capacitors filter distortion to circuit parameters are derived. Design techniques for low-distortion applications are discussed and are applied to a sixth-order experimental filter. The filter design uses a fully differential class A/B op amp with a continuous-time common-mode feedback circuit. Distortion measurements show that for 82-dB dynamic range (relative to noise floor) the total harmonic distortion of 0.02% within the whole 4-kHz bandwidth and 0.07% within 20-kHz bandwidth.