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Simple Voltage Follower Block Having High Precision with Low Die Size

IP.com Disclosure Number: IPCOM000012674D
Publication Date: 2003-May-20
Document File: 3 page(s) / 117K

Publishing Venue

The IP.com Prior Art Database

Abstract

Integrated circuits (IC) that provide an integrated voltage follower or voltage-to-current conversion are common. Precise voltage followers are usually based on operational amplifier structures which require frequency compensation. Such compensation circuitry consumes a great deal of die space and thus requires large die size. In contrast, simple voltage followers occupy very small die size, however their precision and linearity is poor. Therefore, it would be desirable to devise a new circuit having high precision and low die size.

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Simple Voltage Follower Block Having High Precision with Low Die Size

Integrated circuits (IC) that provide an integrated voltage follower or voltage-to-current conversion are common.� Precise voltage followers are usually based on operational amplifier structures which require frequency compensation. � Such compensation circuitry consumes a great deal of die space and thus requires large die size. In contrast, simple voltage followers occupy very small die size, however their precision and linearity is poor.�

Therefore, it would be desirable to devise a new circuit having high precision and low die size.

Detailed Description

Referring to figure 1, a new two transistor voltage follower structure is shown in which both transistors have a similar voltage shift dependent on the output current.� The output current IOUT is mirrored through transistors M6, M5 to the emitter of transistor Q3 (current IS). � The mirror factor (N) is not critical for DC transfer, however should be >1 for stability. � Since the current IST (start-up current) is very small, current through Q3 is given just by the IS. � VBE3 of Q3 and VBE4 of Q4 are then well compensated since their DVBE voltages (due to changing output current) are identical. � Identical value of VBE3 and VBE4 can be achieved by sizing of Q3, Q4 and by the mirror factor N. � The only error is based on the mismatch between VBE3 and VBE4 voltages and by the different temperature coefficient of VBE3 and VBE4.� This system is stable with...