M Tech Dissertations

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Subject: search.filters.subject.Switched capacitor circuits

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    Capacitor mismatch in switched capacitor circuits, techniques to minimize mismatch
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2011) Chevella, Subhash; Parikh, Chetan D.
    This thesis about the designing of capacitive mismatch insensitive switched capacitor amplifier for analog to digital converters (ADC). The accuracy of the conversion is an important factor. The accuracy depends upon the residue amplifier used in the designing of the pipelined ADC. So, designing of accurate gain switched capacitor (SC) amplifier is an important concern. The gain accuracy of SC amplifier depends upon the MOS switches, capacitance mismatch and operational amplifier. Among these three, the accuracy will be affected more due to the mismatch of the capacitance values. This thesis is more concentrated on capacitance mismatch. I proposed a switched capacitor amplifier whose gain is less sensitive to capacitance mismatch as compared to conventional switched capacitor amplifier. The percentage of error variation of the gain due to mismatch in proposed circuit varies from 2.1% to 2.9% but in conventional amplifier it varies from -5.1% ~ 8.5%. Proposed circuit has an improvement of 5.6%. All these simulation have done using 180nm technology in LT Spice.
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    Adaptive biased switched capacitor filters
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Bajaj, Garima; Parikh, Chetan D.
    The demand from today’s handheld devices, such as laptop, ipod, cellphones is to have a long battery life with no compromises in speed. The devices dissipate power even in standby mode also. Op-amp is a major block in all these devices. Its application in these devices may be as an amplifier, filter, A/D or D/A convertor. In most of the cases the op-amp may be in standby mode with no input signal. Power dissipated in these standby periods is wasted, and this is of concern for two reasons. First, in battery powered equipment, supply power must be conserved to extend the battery life. Second, any power wasted in the circuit is dissipated in the active devices which mean that they operate at higher temperatures and thus have a greater chance of failure. So the point of major concern is to reduce power in standby modes, and to give high speed when the device is operating. This research work makes an attempt to design the most common application of Op-amp, a filter, such that it consumes low power with no compromise in speed. It ensures that the load capacitor of op-amp settles to the final value at a much faster speed, and at the same time consuming less power in stand by mode. The filter is designed for a cut off frequency of 100KHz at 2.5V in 0.18μm technology. The filter with a higher cut off frequency requires higher current and thus results in large power dissipation. The two Op-amps discussed, are proved and verified that they consume very less power for such a high cut off frequency.
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    Tool to calculate the width and length of capacitor for switched-capacitor band pass filter
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2007) Doshi, Kaushal J.; Nagchoudhuri, Dipankar
    The switched capacitor (SC) circuits find their applications in many fields. Due to their lower size at low frequencies, higher density can be achieved compared to active RC counterparts. Still there are nonlinerarities in SC circuits, many which are due to error in fabrication process. As will be explained later, the performance of SC circuits depends on capacitance ratios instead on absolute values; hence as designer, we are interested in matching the capacitance ratios rather than absolute values.

    This tool which we designed takes care that the width and length of the capacitors it gives as output, has area ratios and perimeter ratios equal for all capacitor pairs, thus taking care of the proper matching of all capacitor.