Resistance-free relaxation oscillator based on capacitor plate exchange

Abstract

The invention discloses a resistor-free relaxation oscillator based on capacitor plate exchange. The resistor-free relaxation oscillator comprises a PTAT current source circuit, a double PTAT voltage generation circuit, a plate exchange capacitor charging and discharging circuit and a pulse generation circuit, the output end of the PTAT current source circuit is connected with the input end of the double-PTAT voltage generation circuit and the first input end of the polar plate exchange capacitor charging and discharging circuit. The first output end of the double-PTAT voltage generation circuit is connected with the second input end of the polar plate exchange capacitor charging and discharging circuit, and the second output end of the double-PTAT voltage generation circuit is connected with the first controlled end of the pulse generation circuit; and a first controlled end and a second controlled end of the polar plate exchange capacitor charging and discharging circuit are respectively connected with a first control end and a second control end of the pulse generation circuit. By adopting the embodiment of the invention, the relaxation oscillator is realized under a resistor-free capacitor plate exchange circuit structure, and the production cost is saved while the low delay is ensured.

Description

technical field [0001] The invention relates to the field of integrated circuit design, in particular to a non-resistance relaxation oscillator based on capacitive plate exchange. Background technique [0002] In a system on chip, the system clock source of the digital circuit is usually a crystal oscillator, a fully on-chip ring oscillator or a fully on-chip relaxation oscillator. Crystal oscillators are often used in systems with wireless communication or high-speed interfaces, and their frequency stability is high, while their power consumption and cost are high; ring oscillators are usually used in high-frequency digital systems, their resonance frequency is high, but the frequency Poor stability and high power consumption; relaxation oscillators are usually used in low-frequency digital systems. Although their frequency stability is low, they have low power consumption, simple structure, high frequency-temperature stability, and low cost. Advantages, especially for ult...

AI Technical Summary

Problems solved by technology

The first is the delay T r There is a contradiction with the discharge operation of the switch SW. If in order to obtain an accurate clock frequency, it is necessary to reduce the delay T of the comparator as much as possible r , but the extremely low delay T r It will cause the positive pulse time to be too short, and the short positive pulse time will cause the switch SW to fail to switch V C Bleed to V SS1 Afterwards, the comparator COMP feeds back a new closing signal, thereby shortening the width of the next clock cycle

In order to solve the problem of insufficient discharge, a delay chain is usually added behind the comparator, but the delay of the inverter delay chain is just a nonlinear function of time, thus deteriorating the frequency-temperature stability of the oscillator , that is, larger loop delays result in lower frequency-temperature stability and larger layout area at low output frequencies

The second is that it is difficult for the oscillator to achieve a very low resonance frequency, because T1=T r +T C =T r +RC, in order to reduce the frequency, you need to increase R or C or increase R and C synchronously. You can also use a multi-stage frequency divider in the subsequent stage to obtain a low-frequency clock, but for IoT and other systems, if you use a frequency divider to obtain low-frequency clock, the original high-frequency oscillator and frequency divider will consume a large amount of current, resulting in a sharp increase in power consumption; if the RC value is increased instead of the frequency divider, the space required for passive components will be reduced Consumes a huge layout area and increases the cost of producing chips

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