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A STARTUP CIRCUIT FOR VOLTAGE & CURRENT REFERENCES WITH ZERO STEADY STATE CURRENT

IP.com Disclosure Number: IPCOM000007583D
Original Publication Date: 2002-Apr-08
Included in the Prior Art Database: 2002-Apr-08
Document File: 3 page(s) / 123K

Publishing Venue

Motorola

Related People

Sanjay Kumar Wadhwa: AUTHOR [+2]

Abstract

A startup circuit that supplies current to a Beta multiplier reference circuit is presented. At the time of starting of a reference circuit, the startup circuit provides startup current so that the reference circuit is brought to its desired operating state. In the steady state, when the reference circuit has stabilized at its desired operating condition, the startup circuit draws no supply current. Thus, it is particularly useful for low power ICs that contain a voltage or current reference circuit. The startup circuit uses feedback from the reference circuit to make sure that the reference circuit has reached its desired operating condition prior to shutting itself off.

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A STARTUP CIRCUIT FOR VOLTAGE & CURRENT

REFERENCES WITH  ZERO STEADY STATE CURRENT

Sanjay Kumar Wadhwa

Gurgaon, Haryana

A startup circuit that supplies current to a Beta multiplier reference circuit is presented.  At the time of starting of a reference circuit, the startup circuit provides startup current so that the reference circuit is brought to its desired operating state.  In the steady state, when the reference circuit has stabilized at its desired operating condition, the startup circuit draws no supply current.  Thus, it is particularly useful for low power IC’s that contain a voltage or current reference circuit.  The startup circuit uses feedback from the reference circuit to make sure that the reference circuit has reached its desired operating condition prior to shutting itself off.

In VLSI chips that use a voltage or current reference circuit to generate bias voltages or currents for different blocks of the chips, a startup circuit is normally used to provide startup current to the reference circuit so that when the power to the chip is switched on, then in the steady state, the reference circuit will settle to its desired operating state.  Without a startup circuit, it may happen that the reference circuit may not start at all and thus, it will draw no current from the supply and the bias voltages will settle at the respective power supply voltages (i.e., PBIAS will settle at VDD and NBIAS will settle at VSS).  Therefore, startup circuits play a very important role of bringing the reference circuits to their required operating condition.  However, it is very much desirable that the startup circuit ideally should consume no steady state current once the reference circuit reaches its desired operating state.  This is particularly important in low power IC’s where continuous current drain by the startup circuit reduces the battery life.  The proposed startup circuit addresses this problem.  It is turned off once the reference circuit starts working properly so that it draws practically zero supply current and thus battery life can be enhanced.

            A Beta multiplier reference circuit along with the proposed startup circuit has been shown in the figure 1.  The reference circuit is made up of two PMOS transistors M0 and M1, two NMOS transistors M2 and M3, and a resistance R0.  M0 and M1 are equal in size and they act as a current mirror.  The size of M2 is more than the size of M3 and therefore for the same current in M2 and M3, the gate to source voltage for M2 will be less than that of M3.  This difference in their gate to source voltages is applied across the resistance (R0), which generates the required current given by,

                                                     Iref = {Vg...