A 1.8V supply multi-frequency digitally trimmable on-chip IC oscillator with low-voltage detection capability

ABSTRACT

The design of a 1.8V power supply, multi-frequency on-chip IC oscillator with a built-in low voltage detection (LVD) circuitry is described. Since the modules share the same bandgap cell, the system includes a new bandgap isolation strategy based on wide swing cascode current mirrors to reduce noise coupling into the LVD. The IC oscillator generates four selectable clock frequencies: 4MHz and 8MHz from 1.8V to 5.5V, 12MHz and 22MHz from 2.7V to 5.5V. After fine-tuning the oscillator via digital trimming its output frequency varies less than ±2.5% around the target frequency over supply ranges and from -40 to 125°C. The measured clock jitter is below 0.1% whereas the recover time from stop is 5μs. The low voltage detection circuit monitors the supply voltage applied to the system and generates the appropriate warning or even initiates a system shutdown before the in-circuit SoC presents malfunction. The module was implemented in a 0.5μm CMOS technology, occupies an area of 360 x 530μm² and requires no external reference or components.

REFERENCES

• 1: Johns, D.A., and Martin, K., Analog Integrated Circuit Design, John Wiley & Sons, 1997.
• 2: Grebene, A.B., Bipolar and MOS Analog Integrated Circuit Design, John Wiley & Sons, 1984.
• 3: A. Olmos, A Temperature Compensated Fully Trimmable On-Chip IC Oscillator, Proceedings of the 16th symposium on Integrated circuits and systems design, p.181, September 08-11, 2003
• 4: Olmos, A., Gomes A., Takiguti R., Clayton F., "A bandgap adjustment strategy for temperature centering and spread reduction", Proc. SBMicro 2001, pp. 82--86, September 2001.
• 5: Babanezhad, J.N., and Gregorian, N., "A Programmable Gain/Loss Circuit," IEEE J. of Solid-State Circuits, Vol. 22, no 6, pp. 1082--1090, December 1987.

INDEX TERMS

Primary Classification:
  B. Hardware
  B.7 INTEGRATED CIRCUITS
      B.7.1 Types and Design Styles
          Subjects: Microprocessors and microcomputers

Additional Classification:
  B. Hardware
  B.7 INTEGRATED CIRCUITS
      B.7.2 Design Aids
          Subjects: Simulation

General Terms:
Design, Experimentation

Keywords:
bandgap, low-voltage detector, oscillator, relaxation, trimming