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High PSRR apparatus for Linear Voltage Regulators

IP.com Disclosure Number: IPCOM000011834D
Publication Date: 2003-Mar-19
Document File: 9 page(s) / 118K

Publishing Venue

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Abstract

Key words: PSRR, Line Regulation, Linear Voltage Regulator, Low Voltage

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High PSRR apparatus for Linear Voltage Regulators

Key words:  PSRR, Line Regulation, Linear Voltage Regulator, Low Voltage

Background

Voltage regulators used with portable battery-powered devices must have high Power Supply Rejection Ratio (PSRR), which guarantees an output voltage with good rejection to supply fluctuations and spikes.  PSRR specifications are often given at the frequency of one kilo hertz (KHz), or in the form of a diagram (refer to Fig. 1) showing suppression (dB) versus frequency.

FIG. 1

Typical wireless applications manage Radio Frequency (RF) sections using multi band selection in combination with a frequency synthesizer, and a power supply reference having about 70 dB noise suppression.  Unfortunately, such suppression, while typical of prior art, is not sufficient to guarantee good quality of signals under varying conditions.  Furthermore, the voltage regulator circuits used must provide a precise voltage reference output independent of temperature, charge or power supply voltage variations.  It is also desirable to provide increased power supply rejection without affecting the minimum voltage supply provided to the voltage regulator, or increasing silicon area by using a high device count solution. 

Prior art is very rich in circuits showing improved PSRR performance.  For example, U.S. Patent 5,694,031 shows a voltage regulator with an accurate reference voltage, and a large swing in the supply voltage wherein the band-gap reference and the error amplifier is supplied with the output regulated voltage instead of Vcc.  Another U.S. Patent 6,118,266 discloses a complex structure using a cascode over Miller compensation scheme for improved PSRR versus frequency.  U.S. Patent 5,512,817 shows a bandgap voltage generator providing a signal amplified by a high gain amplifier which regulates the voltage supplied from the power supply Vdd to the bandgap.  U.S. Patent 5,939,867 discloses the principle of increasing the supply current of the amplifier proportionally with the output current of the regulator.  This pushes the dominant pole of the system to higher frequency, thus PSRR starts to increase at higher frequency.

All of the prior art mentioned above suffer from at least several limitations including requiring supply voltages of more than two volts, and offering little improvement of PSRR at low frequency or when a low amount of load current is supplied by the regulator.  Therefore, there is a need for a correction method and circuit to provide high PSRR of voltage regulators or regulator references that operate at low voltage and operating over a broad range of diverse supply voltages.

Detailed Description of the Invention


The invention is based on the concept of inje...