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Amplifiers and Feedback
Published in David Crecraft, David Gorham, electronics, 2018
The open loop gain of an amplifier, denoted by Av, is the gain before feedback is applied.The closed-loop gain, G, is the gain with feedback, i.e. when the feedback loop is ‘closed’.The loop gain depends on the feedback fraction β and the open-loop gain. When the feedback is connected to the inverting input of an op amp, the | loop gain is −βAV.The feedback fraction, β, is the proportion of the ! output that is fed-back to the input.The closed-loop gain is equal to the open-loop gain multiplied by 1/(1 + βAV) where (1 + βAV) is the feedback factor. The feedback factor can also be expressed as (1 – loop gain).
CMOS Amplifiers
Published in Tertulien Ndjountche, CMOS Analog Integrated Circuits, 2017
Typically, amplifiers should exhibit a high open-loop gain and a high bandwidth to minimize errors in the output voltage. The high gain requirement can be met by cascading gain stages, the number of which is limited by the need for frequency compensation to enable stable feedback. The gain enhancement technique can also be implemented by inserting each cascode transistor in an amplifier feedback path to increase the overall output resistance.
Compensation and Stability
Published in Douglas Self, Audio Power Amplifier Design, 2013
Amplifiers with two-pole compensation are only conditionally stable; when the open-loop gain is effectively reduced by clipping, current-limiting, slew-limiting, or at power-up/down they may show instability. I have not at the time of writing put a two-pole amplifier into quantity production.
Single-ended amplifier-based touch readout circuit with immunity to display noise
Published in Journal of Information Display, 2023
If the open-loop gain of the amplifier (A) for ΔVCOM is not much high, α in (14) is smaller than one and is multiplied to the power of N, which suppresses the display noise. Whereas, in the case of conventional single-ended amplifier-based readout circuit, ΔVOUT for all channels is the same as when N = 1 in (14), ΔVOUT for ΔVCOM of the proposed circuit decreases with N. On the other hand, ΔVOUT for ΔVTX can be easily obtained from (14) by substituting the injected charge due to display noise (CDΔVCOM) with the injected charge due to ΔVTX (CMΔVTX). Since the frequency of the ΔVTX is higher than ΔVCOM, the open-loop gain of the amplifier (A) for ΔVTX is higher than the open-loop gain (A) for ΔVCOM. If A is sufficiently high, α for ΔVTX is close to one, and the signal due to ΔVTX is not suppressed. Meanwhile, ΔVOUT for ΔVTX of the proposed circuit which is the touch signal is similar to that of the conventional circuit, thus the output of the proposed circuit depends on the mutual-capacitance (CM), not the difference of the mutual-capacitances of the adjacent RX lines.
Performance optimization of energy harvesting solutions for 0.18um CMOS circuits in embedded electronics design
Published in Cogent Engineering, 2020
The basic circuit implementing such a feature is shown in Figure 15. where RL can be any load. When the input voltage is negative, there is a negative voltage on the diode, so it works like an open circuit, no current flows through the load, and the output voltage is zero. When the input is positive, it is amplified by the operational amplifier, which switches on the diode. Current flows through the load and, because of the feedback, the output voltage is equal to the input voltage. The actual threshold of the super diode is very close to zero, but is not zero. It equals the actual threshold of the diode, divided by the gain of the operational amplifier. This configuration has a problem, so it is not commonly used. When the input becomes negative, the operational amplifier runs open-loop, as there is no feedback signal through the diode. For a typical operational amplifier with high open-loop gain, the output saturates. If the input then becomes positive again, the op-amp has to get out of the saturated state before positive amplification can take place again. This change generates some ringing and takes some time, greatly reducing the frequency response of the circuit.
A micropower analogue front end for wireless ECG system
Published in International Journal of Electronics Letters, 2018
Yishan Wang, Ralf Wunderlich, Stefan Heinen
where is the open-loop gain of Gm. According to the capacitances of and , the gain of the CCIA is set to 100. Gm is implemented as a folded-cascode amplifier, which is shown in Figure 4. To achieve high power efficiency and high gain at the same time, the input PMOS transistors operate in weak inversion. The differential gains of the CCIA are shown in Figure 5. The common mode feed back circuit is used to decrease common mode gain.