By Vincenzo Peluso
Design of Low-Voltage Low-Power CMOS Delta-Sigma A/D Converters investigates the feasibility of designing Delta-Sigma Analog to electronic Converters for terribly low offer voltage (lower than 1.5V) and coffee strength operation in regular CMOS methods. the selected means of implementation is the Switched Opamp procedure which supplies Switched Capacitor operation at low offer voltage with no the necessity to practice voltage multipliers or low VtMOST units.
a mode of imposing the vintage unmarried loop and cascaded Delta-Sigma modulator topologies with part hold up integrators is gifted. these topologies are studied for you to locate the parameters that maximise the functionality by way of top SNR. in accordance with a linear version, the functionality degradations of upper order unmarried loop and cascaded modulators, in comparison to a hypothetical perfect modulator, are quantified.
an outline of low voltage Switched Capacitor layout strategies, comparable to using voltage multipliers, low VtMOST units and the Switched Opamp strategy, is given. An in-depth dialogue of the current prestige of the Switched Opamp strategy covers the single-ended unique Switched Opamp approach, the converted Switched Opamp process, which permits reduce provide voltage operation, and differential implementation together with universal mode regulate ideas.
the limitations imposed at the analog circuits through low provide voltage operation are investigated. numerous low voltage circuit construction blocks, a few of that are new, are mentioned. a brand new low voltage category AB OTA, in particular suited to differential Switched Opamp functions, including a typical mode suggestions amplifier and a comparator are provided and analyzed.
As a part of a scientific top-down layout strategy, the non-ideal cost move of the Switched Opamp integrator mobilephone is modeled, established upon a number of types of the most opamp non-ideal features. Behavioral simulations performed with those types yield the mandatory opamp requisites that make sure that the meant functionality is met in an implementation.
an influence intake research is played. The impression of all layout parameters, specially the low strength provide voltage, is highlighted. layout directions in the direction of low energy operation are distilled.
implementations are offered including size effects. the 1st one is a single-ended implementation of a Delta-Sigma ADC working with 1.5V offer voltage and eating a hundred &mgr;W for a seventy four dB dynamic diversity in a 3.4 kHz bandwidth. the second one implementation is differential and operates with 900 mV. It achieves seventy seven dB dynamic variety in sixteen kHz bandwidth and consumes forty &mgr;W.
Design of Low-Voltage Low-Power CMOS Delta-Sigma A/D Converters is key interpreting for analog layout engineers and researchers.
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Extra resources for Design of Low-Voltage Low-Power CMOS Delta-Sigma A/D Converters
The clock amplitude should be small to reduce efficiency loss due to Cs • In order to achieve a certain output voltage the number of stages N should be increased. From the last column 36 Low-Voltage Low-Power ~I: AID Converters V;. 6. A Voltage Doubler. is it clear that N should be low, because each stage causes losses. So there exists an optimum for • V~ and N. For very low voltage applications the Dickson multiplier will become very inefficient. g. 3 V would be about 8. In that case the last term in the expression becomes very large.
Inside the dotted line ellipse, the added offset adjust capacitor CCM and switches can be seen. In order to remove the DC component of Cs it is necessary to introduce a second reference level: VREF,hi and also the use of the pMOST as an additional switch device.
Surprisingly another combination of parameters that offers the same perfonnance exists, namely b l equal 3. with the other parameters unchanged. :\1: MODULATOR TOPOLOGIES 25 This is striking because such a good performance is not expected for these parameters. When b l equals 3 (instead of 2). too much output signal is being subtracted. 5 (instead of ±1). This means that this stage is being overloaded. One possible explanation might be that the statistics of the input signal to the second stage have a self stabilizing effect.