Input referred noise gain differential amplifier

A new methodology based on the concept of figure of merit under area constraints is described for designing optimum performance differential amplifiers. First a figure of merit is introduced that includes the three performance parameters, namely, input-referred noise, differential dc gain, and unity-gain bandwidth. Expressions for these parameters have been derived analytically and finally arrived at an expression for the figure of merit. Next it is shown how these performance parameters vary with the relative allocation of the total available area between the input and load transistors.

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Content:

• Figure-of-Merit-Based Area-Constrained Design of Differential Amplifiers
• Pam4 Driver
• Noise Analysis Using Analog Devices Operational Amplifiers in Multisim
• Deliver the lowest distortion and noise in a low-power, wideband, ADC interface (Part 1 of 4)
• Calculating noise figure in op amps
• Rf Harmonics Calculator
• Low-Cutoff Frequency Reduction in Neural Amplifiers: Analysis and Implementation in CMOS 65 nm
• LT1999CS8-10#TRPBF
• Introduction: PID Controller Design

WATCH RELATED VIDEO: 167. Noise: Noise in simple amplifiers, Input Referred voltage and Current Noise

Figure-of-Merit-Based Area-Constrained Design of Differential Amplifiers

Scaling down technology demotes the parameters of AC-coupled neural amplifiers, such as increasing the low-cutoff frequency due to the short-channel effects. To improve the low-cutoff frequency, one solution is to increase the feedback capacitors' value.

This solution is not desirable, as the input capacitors have to be increased to maintain the same gain, which increases the area and decreases the input impedance of the neural amplifier.

We analytically analyze the small-signal behavior of the neural amplifier and prove that the main reason for the increase of the low-cutoff frequency in advanced CMOS technologies is the reduction of the input resistance of the operational transconductance amplifier OTA.

We also show that the reduction of the input resistance of the OTA is due to the increase in the gate oxide leakage in the input transistors. In this paper, we explore this fact and propose two solutions to reduce the low-cutoff frequency without increasing the value of the feedback capacitor. The first solution is performed by only simulation and is called cross-coupled positive feedback that uses pseudoresistors to provide a negative resistance to increase the input resistance of the OTA.

As an advantage, only standard CMOS transistors are used in this method. Simulation results show that a low-cutoff frequency of 1. In addition, the power consumption is 0. Measured results are obtained by in vitro recordings on slices of mouse brainstem. The measurement results show that the bandwidth is between 2 Hz and 5. The neural amplifier has The measurement results show an input-referred noise of 6.

Neural signal acquisition has a crucial role in understanding the function of the different parts of the brain as well as exploring and treating its various disorders Stevenson and Kording, In addition, this data is used in developing the neural prostheses Sun et al.

This is why the demand for new techniques that enable monitoring brain activity wirelessly through implantable devices is increasing every day Schwartz et al. A complete review on neural recording is given in Hashemi Noshahr et al.

Brain signals are very small and have very low bandwidth. Increasing the number of the neural recording sites, which are called channels, is required in some applications, as the spatial resolution of the capturing signals increases. As an example, the total number of channels reported in Musk is The electrochemical reaction at the electrode-tissue interface in each channel generates different DC offset voltages across the various electrodes.

These voltages vary typically between 1 and 10 mV and in some cases up to 50 mV Bagheri et al. As the offset voltages of the channels have high value, they can saturate the neural amplifier. Therefore, they should be eliminated. On the other hand, there is an alternative method that blocks these DC offset voltages by using a low-pass filter in the feedback path, which is called DC-coupled input offset rejection.

The authors in Enz et al. To design multichannel neural amplifiers, the following factors should be considered and diminished as much as possible. Power consumption: the brain tissues that are surrounded by implantable neuro-amplifiers must be protected from heat damage.

For this purpose, the power dissipation of these amplifiers must be lowered. Chip area: The neural amplifiers are generally huge. This is because they usually utilize large AC-coupled input capacitors. Also, to decrease the flicker-noise power of amplifiers, the size of the MOS transistors is designed to be very large especially in the differential pairs. Therefore, for a specific chip area, to maximize the number of the channels, the amplifiers should be designed in their minimum area.

Noise: the neural signals have very low amplitude and bandwidth. The flicker and thermal noise of the neural amplifier circuit is the main source of the noise, which can decrease the signal to noise ratio SNR in the output of the amplifiers.

This is why they are designed as a low noise amplifier LNA. In the low frequency, the power of the flicker noise is dominant. To decrease the flicker-noise power, in addition to increasing the size of the transistors and utilizing a PMOS differential pair, the chopper-stabilization technique is used Denison et al.

The chopper-stabilization technique modulates the low-frequency noise of the OTA flicker noise , as well as the offset voltage to a higher frequency by the chopper switches.

These higher frequencies are eliminated with a low pass filter LPF. The 65 nm CMOS and finer technologies introduce new challenges as a result of the short channel effects for analog circuits. One of these challenges is decreasing the transconductance gm of MOS transistors, which diminishes the voltage gain of the whole amplifier. This can be resolved by designing the neural amplifier in 2 or 3 gain stages Zou et al. The other destructive effect of short channel effects is increasing the low-cutoff frequency f L of the AC-coupled neural amplifiers.

In this paper, we analyze the parameters that affect the low-cutoff frequency and propose two solutions. The first solution utilizes a standard CMOS and improves the low-cutoff frequency by increasing the input resistance. The second method utilizes thick-oxide transistors to increase the input resistance. The rest of the paper is organized as follows.

Section II analyzes the low-cutoff frequency in neural amplifiers. Section III presents the two proposed solutions. The experimental results are provided in Section IV and the paper concludes in section V. Figure 1 shows the schematic of a fully differential neural amplifier with conventional capacitive feedback network CFN architecture.

As explained in Harrison and Charles , this architecture is one of the most popular architectures of AC-coupled neural amplifiers in terms of low power consumption, low noise, and compact area. Figure 2 shows the frequency response of this CFN neural amplifier as a bandpass amplifier. Assuming that the voltage gain of the operational transconductance amplifier OTA is significantly high, the voltage gain of the amplifier in the midband A M can be approximately calculated by.

Also, the low-cutoff frequency f L of the amplifier can be approximated as. However, by increasing C F , it is required to increase C I to maintain the same gain which results in huge area loss for each channel of a multi channel device.

In addition, this results in the reduction of the input impedance of the neural amplifier. MOS pseudoresistors can be utilized as a feedback resistance R F for their compactness and high resistance. However, the drawback of this technique is that the MOS pseudoresistors provide much less resistance in advanced technology.

For example, in an old technology such as 1. To better understand the effects that increase the f L value in the advanced CMOS technologies, we provide a small signal analysis of the amplifier in the following. The equivalent small signal half-circuit of a neural amplifier of Figure 1 is depicted in Figure 3.

The OTA can be modeled as a single pole amplifier with a pole at the output node. We extract the time constant of the first pole as. Reduction of the oxide thickness in advanced technologies translates to lower input resistance i. By increasing G i , the denominator in Equation 3 grows much faster than the numerator. However, for older technologies, we can simplify Equations 3 to 4 with the assumption that OTA's input resistance R i is infinity i.

Figure 4 illustrates the frequency response of the small signal model of the amplifier shown in Figure 3 for different values of R i. The DC voltage of the outputs is biased at 0. As shown in this figure, f L decreases by increasing R i. Figure 4. Simulation of frequency response of a neural amplifier with various amounts of R i. Figure 6 shows two implementations of the CCPF connections far and close connections in which each pseudoresistor is implemented with a standard PMOS transistor.

Figure 5. The neural amplifier with cross-coupled positive feedback architecture. Figure 7 shows the small signal equivalent circuit of the neural amplifier with a far CCPF connections. For simplicity of calculation, we assume all the pseudoresistors are identical and have the same value.

Figure 7. Small signal equivalent circuit of the neural amplifier with a CCPF connection. By considering Equation 10 , R N can be presented as.

In practice, the values of the pseudoresistors are not equal and vary based on their currents or their voltages. Therefore, Equation 11 is not accurate and simulation results are required to calculate the exact value of R N.

In order to decrease the total capacitance, we exploited a T-capacitor feedback network shown in Figure 8 Ng and Xu, The midband gain of the amplifier in Figure 8 is calculated as. We can adjust the capacitances in Equation 12 to keep the total capacitance of the OTA low while maintaining the same gain. Figures 9 , 10 illustrates the frequency response of the amplifier in terms of gain and phase, respectively, and in in far, close, and no CCPF connections. The amount of the low-cutoff frequency for far, close, and no CCPF connections are 1.

Figure 9. Simulation of frequency response gain of the amplifier of Figure 8 with far, close and no CCPF connection. Figure Simulation of frequency response phase of the amplifier of Figure 8 with far, close and no CCPF connection. The positive feedback in the CCPF architecture of the amplifier can result in instability. However, by carefully designing the number of pseudoresistors, transistor sizes, and the position of the CCPF connection we can make sure that the negative feedback is dominant and the whole architecture is stable and satisfies at least a 60 degree phase margin.

Figure 11 shows the simulation of open loop frequency response of the amplifier of Figure 8 with 70 degree phase margin. Simulation of open loop frequency response gain and phase of the amplifier of Figure 8 with 70 degree phase margin. By adding switches to the CCPF connection we can program i. In case of multiple pseudoresistors e.

Pam4 Driver

Also, for convenience , the extensive references for all four parts are repeated as a group at the end of each part. This discussion will step through a simple input-side interface to the FDA that offers numerous benefits for an AC coupled, communications oriented, ADC interface requirement. It will then describe output-side interstage-coupling options to translate the FDA output signal to the ADC with a controlled noise power bandwidth. Moving from this characterization condition of lab signal sources, and narrowband filters, to systems requiring a broadband final stage with gain requires a careful consideration of the expected FFT degradation.

Noise Analysis Using Analog Devices Operational Amplifiers in Multisim

Noise, composed of small, random voltages, can be difficult to measure. Lab instruments add their own noise, further complicating the measurement. Special techniques are often used when measuring noise. For example, amplifiers are typically configured with high closed-loop gains, multiplying their input noise to make it easier to measure. Low-fixed-gain differential amplifiers present a greater challenge, however, as their integrated feedback and gain resistors preclude the use of a high-gain configuration. Additionally, differential-to-single-ended conversion is needed to interface with available spectrum analyzers. A second amplifier stage can provide gain and the differential-to-single-ended conversion, neatly solving both of these problems. Figure 1 shows an ADA selectable-gain 1, 2, or 3 differential amplifier followed by an AD low-noise, low-distortion op amp.

Deliver the lowest distortion and noise in a low-power, wideband, ADC interface (Part 1 of 4)

In this tutorial we will introduce a simple, yet versatile, feedback compensator structure: the Proportional-Integral-Derivative PID controller. The PID controller is widely employed because it is very understandable and because it is quite effective. One attraction of the PID controller is that all engineers understand conceptually differentiation and integration, so they can implement the control system even without a deep understanding of control theory. Further, even though the compensator is simple, it is quite sophisticated in that it captures the history of the system through integration and anticipates the future behavior of the system through differentiation.

Calculating noise figure in op amps

Scaling down technology demotes the parameters of AC-coupled neural amplifiers, such as increasing the low-cutoff frequency due to the short-channel effects. To improve the low-cutoff frequency, one solution is to increase the feedback capacitors' value. This solution is not desirable, as the input capacitors have to be increased to maintain the same gain, which increases the area and decreases the input impedance of the neural amplifier. We analytically analyze the small-signal behavior of the neural amplifier and prove that the main reason for the increase of the low-cutoff frequency in advanced CMOS technologies is the reduction of the input resistance of the operational transconductance amplifier OTA. We also show that the reduction of the input resistance of the OTA is due to the increase in the gate oxide leakage in the input transistors.

Rf Harmonics Calculator

The required high sensitivity of the analog signal conditioning path dictates having a high sensitivity at the front-end while the Input-Referred Noise IRN is kept low. Therefore, a TIA with a high sensitivity to detected current bio-signals is provided by a photodiode module. Gain adjustment is implemented by a coarse-gain-step using selective loads with four different gain values and fine-gain steps by 42 dB dynamic range during 16 fine steps. The settling time of the TIA is compensated using a capacitive compensation which is applied for the last stage. An off-state circuitry is proposed to avoid any off-current leakage.

Low-Cutoff Frequency Reduction in Neural Amplifiers: Analysis and Implementation in CMOS 65 nm

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LT1999CS8-10#TRPBF

RELATED VIDEO: 176N. Intro. to amplifier noise, output noise, and input-referred noise

Noise Analysis is a small signal analysis which is carried out at discrete frequencies using a linearized version of the circuit. The mechanics are very similar to those of an AC analysis. The key difference is that in AC analysis the signal generators are AC signal sources explicitly defined by the user whereas in noise analysis the signal generators are invisible noise sources attached to every noise-generating element in the circuit, such as to the resistor shown below:. Additionally, in AC analysis the AC signal source amplitude and direction are set explicitly by the user while in noise analysis the amplitude of the noise source is set through a formula representing the physical noise phenomena of the noise-generating element.

Introduction: PID Controller Design

Instructor: Professor Ali Hajimiri. The subject of this course is the analysis and design of analog integrated circuits at the transistor level, with an emphasis on intuitive design methods, quantitative performance measure and practical circuit limitations. The course deals with analog circuits in which the information is represented by signals that are continuous both in time and amplitude. Circuit performance is evaluated by means of hand calculations and computer simulations. Topics include: review of physics of bipolar and MOS transistors, low-frequency behavior of single-stage and multistage amplifiers, current sources, active loads, differential amplifiers, operational amplifiers, high-frequency circuit analysis using time- and transfer constants, high-frequency response of amplifiers, feedback in electronic circuits, stability of feedback amplifiers, and noise in electronic circuits, and supply and temperature independent biasing.

All rights reserved. Applications With external gain set resistors, the LMH can be used at any desired gain. Gain flexibility coupled with high speed n Differential AD driver makes the LMH suitable for use as an IF amplifier in n Video over twisted pair high performance communications equipment. Boldface limits apply at the temperature extremes.