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POR circuit with Brown-Out detector

IP.com Disclosure Number: IPCOM000130469D
Publication Date: 2005-Oct-24
Document File: 8 page(s) / 3M

Publishing Venue

The IP.com Prior Art Database

Related People

G.K. Siddhartha: AUTHOR [+3]

Abstract

A Power on reset (POR) circuit with Brown out (BO) detector having thresholds independent of supply ramp-rate is proposed. The circuit has been designed in 65nm CMOS process at 1.1V supply. By using hysteresis, it is always ensured that BO threshold is lower than POR threshold. The simulation results show that the POR/BO threshold does not depend upon the supply ramp-rate for fixed PVT corner for large range of supply ramp rates. The circuit has very low current consumption (~4µA) due to which it is ideally suited for low power applications.

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POR circuit with Brown-Out detector

G.K. Siddhartha, Sanjay K. Wadhwa, Anand Gaurav

Abstract

 A Power on reset (POR) circuit with Brown out (BO) detector having thresholds independent of supply ramp-rate is proposed. The circuit has been designed in 65nm CMOS process at 1.1V supply. By using hysteresis, it is always ensured that BO threshold is lower than POR threshold. The simulation results show that the POR/BO threshold does not depend upon the supply ramp-rate for fixed PVT corner for large range of supply ramp rates. The circuit has very low current consumption (~4µA) due to which it is ideally suited for low power applications.

1.             Introduction

 All integrated circuits are required to be brought to a known state during power up. When power supply is ramping up and crosses a level suitable for circuit operation, a Power on Reset (POR) circuit monitoring the power supply asserts a reset. An on-chip POR solution reduces the cost and provides a reliable reset signal. Also, there may be conditions in which the power supply dips (called Brown-Out events) below its operating value such that the circuits can no longer work reliably. Such events are more common in battery operated equipments when battery contact with the terminals connected to chip breaks momentarily due to equipment falling etc. and supply of the chip drops. The POR circuit must be able to detect such events and generate a reset when power supply dips below a certain threshold called Brown-Out Threshold.

The important considerations for a POR/BO design are:

I.                     Cater to wide supply ramp rates (rise and fall): the circuit should be able to work with a wide range (from msec to msec) of supply ramp up and down rates.

II.                   BO Threshold must be lesser than POR threshold: if POR Threshold is not high, there may be a problem in initializing critical circuit elements such as memories. At the same time, BO Threshold has to be lower to avoid any resets during DVFS (Dynamic Frequency Voltage Scaling) mode and DSM (Deep Sleep Mode), where VDD is changed dynamically from one voltage value to the other (such as between 1.2V to 0.8V) to reduce power consumption of the chip. Thus, the POR threshold can be adjusted first as required and BO threshold can be kept lower to meet both the criterion.

III.                 Low power consumption: the circuit should consume as low power as possible (of the order of a few mA). This is very important for portable battery operated equipments.

IV.                 It should be able to work reliably at low supply voltages such as 1.1V for current process technologies like CMOS90 and CMOS65.

V.                   Should consume low die size

2.             Circuit Description

The proposed circuit is shown in Figure 1. The detector comprises of transistors M0 and M1, Resistors R1, R2 and R3 and invertors INV1, INV2 and INV3. 

  Figure 1:  Proposed POR and BO detector circuit

Initially, as VDD starts ramping up from 0V, nodes d1, d2, det_out and POR output, por_out_b will be...