Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-01-28
2001-05-22
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S563000
Reexamination Certificate
active
06236262
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of power supply regulation, and more particularly, to regulated power supplies for low noise microphone preamplifiers.
BACKGROUND OF THE INVENTION
Devices capable of outputting a regulated DC voltage from an unregulated voltage are known for use in an integrated circuit. One example of a known circuit of this type is the “band gap core” circuit, or the “polarization circuit with a reference voltage output by a difference differential” as described in the “Analysis and Design of Analog Integrated Circuits” manual published by Paul T. GRAY and Robert G. MEYER in 1984, second edition under number ISBN 0471-81454 7, pages 4-181 and subsequent pages.
This type of circuit is capable of achieving a noise rejection ratio for noise from an unregulated power supply equal to about 40 to 70 decibels. This ratio is insufficient, particularly in the case of a power supply for a preamplifier for a signal output by the microphone in a camera with a universal standard bus port. In this type of camera, the main power supply has a large amount of noise due to the many sudden changes in power consumption. Typically, the regulated voltage is filtered, for example, using additional R.C. filters, but these filters are not very efficient at the low frequencies present in the audio range. Furthermore, these filters are not necessarily possible on integrated circuit chips.
Another disadvantage of self-polarized circuits like those described in the manual mentioned above, is that the output regulated voltage is necessarily less than the unregulated power supply voltage. Consequently, a sufficiently high unregulated voltage is necessary so that the regulated voltage after division is sufficient to be useable by standard circuits on the load side. This is not always the case, particularly on portable equipment such as cameras.
Accordingly, there is a need for a regulated power supply with a better noise rejection ratio for noise in the unregulated power supply voltage. This ratio is preferably between 100 dB or more. The better noise rejection ratio should also be at low audio frequencies, and the level of this power supply should be sufficiently high for use by these circuits on the load side.
SUMMARY OF THE INVENTION
According to the invention, a conventional reference voltage generating circuit will be used and the voltage obtained at the output will be coupled to the input of an operational amplifier. The output of the operational amplifier will form the unregulated voltage input to the reference voltage generator.
The operational amplifier performs two functions. Firstly, it amplifies the reference voltage at the output from the reference voltage generator. Secondly, it reduces the noise at the input by about 50 decibels. Considering noise specific to components and possibly to an adapter stage between the reference voltage generator and the operational amplifier, it is impossible to expect that the total rejection will be the sum of the rejections, namely about 120 dB. However, it is possible to approach or exceed 100 decibels. Thus, a voltage at a suitable level is available with a noise rejection ratio of noise from the unregulated power supply of about a 100 dB.
The system that has just been described necessitates a startup phase during which the reference voltage generator is powered by the unregulated power supply voltage. This startup phase terminates as soon as the output voltage from the operational amplifier becomes sufficiently large to power the generator in turn. At the end of this startup phase, the power supply for the reference voltage generator is switched from the unregulated power supply voltage to the voltage at the output from the operational amplifier.
In sum, the invention relates to a device for generation of a regulated DC voltage starting from a DC power supply voltage source. The device includes a reference voltage circuit with the DC power supply voltage being applied to one input. The reference voltage circuit supplies an output voltage pre-regulated to a level that is a fraction of the DC power supply voltage equal to or less than 1. The device includes the output from the reference voltage generator circuit carrying the pre-regulated voltage being coupled to a first input to an operational amplifier with a second input and one output. The output carries the regulated DC voltage, and a feedback voltage taken from the output from the operational amplifier is applied to the second input. This output is coupled to the input of the reference voltage generator.
REFERENCES:
patent: 5359552 (1994-10-01), Dhong et al.
patent: 6133779 (2000-10-01), Sichert et al.
patent: 0 434 435 A2 (1990-12-01), None
patent: 0 751 451 A1 (1995-06-01), None
patent: 0 661 616 A2 (1995-07-01), None
Allen, Dyer, Doppelt, Milbraith & Gilchrist, P.A.
Galanthay Theodore E.
STMicroelectronics S.A.
Zweizig Jeffrey
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