Patent Issued for Startup Circuitry and Corresponding Method for Providing a Startup Correction to a Main Circuit Connected to a Startup Circuitry

By a News Reporter-Staff News Editor at Journal of Engineering -- STMicroelectronics Design and Application S.R.O. (Praha, CZ) has been issued patent number 8324944, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventor is Schindler, Jaromir (Hranice n. M., CZ).

This patent was filed on May 25, 2010 and was cleared and issued on December 4, 2012.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present disclosure relates to a startup circuitry connected to a main circuit which has at least an output terminal connected to its feedback terminal by a feedback loop. The disclosure also relates to a method for providing a startup correction to a main circuit connected to a startup circuitry. The disclosure particularly, but not exclusively, relates to a startup circuitry for analog circuits, in particular of the low power type and the following description is made with reference to this field of application for convenience of explanation only.

"As it is well known, self biased circuits, in particular analog ones, need to have a so called startup circuitry able to fast reestablishing a working or operational state when the circuit are connected to a power supply or, in a general manner, when they are enabled to work.

"In particular, circuits with an internal feedback loop, like bandgap reference circuits, DVgs/R reference circuits or current source circuits, which are used widely in nowadays analog integrated circuits, usually have more than one single desired operational status or point.

"Therefore, in this field there is the need of ensuring that a circuit of this kind reaches a right DC operational point, in a safely and reasonably timely manner. This need is satisfied, as already indicated above, by adding a suitable startup circuitry to main circuit.

"A startup circuitry is generally divided in two portions, namely a first or sensing portion that detects whether a main circuit connected to the startup circuit is in a desired operational point (OP) and suitably drives a second or active portion.

"In particular, the active portion of the startup circuitry is configured to force the main circuit to a desired OP, while both the sensing and the active portions should not influence the main circuit when settled in the desired OP.

"A startup circuit of a known type is shown for example in FIGS. 1A and 1B and described in the U.S. Pat. No. 5,867,013 issued on Feb. 2, 1999 in the name of CYPRESS SEMICONDUCTOR CORP. In particular, according to this known solution, the sensing of the OP of a band-gap reference circuit 30 is based on the voltage value Vgs of the NMOS transistor 50 which senses the output band-gap voltage Vout at the node 46. The signal so sensed is shaped and processed by the inverter 56 of the startup circuit 44. Moreover, the output signal from the inverter 56 is provided to an active portion of the startup circuitry 44 essentially comprising the PMOS transistor 64. This active portion forces, in case of a bad operational state of the band-gap reference circuit 30, a positive voltage value to the node 48.

"Another known startup circuitry is shown in FIG. 2. In this case, a branch current rather than a node voltage is checked by the sensing part of the startup circuit to recognize the state of the main circuit, in particular a band-gap circuit. A sensing transistor M1 copies a current signal from the main circuit and compares it with the current supplied by the resistor R3. The active portion of the startup circuit essentially comprises the transistor M2. In case of a wrong OP (when there is no current through the main circuit branches) the transistor M2 starts to sink current and forces the band-gap circuit to the right OP.

"The many different startup circuitries, which are known and widely used in analog circuit design, could be considered as alternative embodiments or improvements of the above described circuitries. Some of them are described for instance in the U.S. Pat. Nos. 6,160,392, 6,084,388, 6,222,399, 6,784,652 and 6,057,721."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "In an embodiment, a startup circuitry is configured to break the feedback loop of a main circuit connected thereto and provide to an output terminal a correct voltage value during the startup phase of the main circuit.

"In an embodiment, a startup circuitry connected to a main circuit which has at least an output terminal connected to its feedback terminal by a feedback loop characterized in that said startup circuitry is connected to the main circuit in such a manner to break the feedback loop, by having a first circuit node connected to said output terminal of said main circuit and a second circuit node connected to its feedback terminal, said startup circuitry providing a correct output voltage value during the startup phase of said main circuit.

"According to an embodiment, the startup circuitry also comprises an auxiliary circuit which may be a functional a copy of said main circuit not suffering from the same startup variations and thus providing said correct output voltage value.

"According to an embodiment, the startup circuitry further comprises a startup detection block connected to a sensing terminal of said main circuit and providing on a third circuit node an enabling signal corresponding to a state of said main circuit wherein a startup is needed.

"According to an embodiment, the startup circuitry further comprises a switching block which is inserted between said first and second circuit node of said main circuit and is connected to a fourth circuit node of said auxiliary circuit providing said correct output voltage value as well to said third circuit node of said startup detection block, said enabling signal being used as a driving signal by said switching block in order to open said feedback loop of said main circuit.

"According to an embodiment, the startup circuitry further comprises a compensation feedback impedance coupled between a fifth circuit node and a first voltage reference, said fifth circuit node being in turn connected to said first circuit node through said switching block in order to be connected to the main circuit when said feedback loop is open. In an embodiment, the switching block comprises a first and a second switch, both driven by said enabling signal provided by said startup detection block, wherein: said first switch is coupled between said first circuit node and said fifth circuit node in a first operational state of the main circuit, and between said first circuit node and said second circuit node in a second operational phase of said main circuit, when said feedback loop is to be closed; and said second switch is coupled between said fourth circuit node and said second circuit node and is closed in said first operational state of said main circuit, when said feedback loop is to be opened, while it is open in said second operational phase of said main circuit, when said feedback loop is to be closed.

"According to an embodiment, said auxiliary circuit is disconnected from a second voltage reference, in said second operational phase of said main circuit, when said feedback loop is closed.

"In an embodiment, said main circuit comprises at least an output driver transistor which is coupled between said second voltage reference and said first circuit node and has a gate terminal connected to an internal circuit node and in said startup detection block is inserted between said first and second voltage references and in turn includes at least a detection transistor which is coupled between said second voltage reference and a detection condenser, in turn connected to said first voltage reference interconnected in correspondence with a detection node, said detection transistor having a gate terminal connected to said internal circuit node.

"In an embodiment, said startup detection block further comprises a first and a second inverter which are inserted, in series to each other, between said detection node and a switching internal circuit node and interconnected in correspondence with said third circuit node.

"In an embodiment, said switching block is inserted between said first and second circuit nodes and includes at least a first switching transistor being coupled, in series with a first current generator, between said first circuit node and said first voltage reference as well as a second switching transistor being also coupled, in series with a second current generator, between said first circuit node and said first voltage reference, said first current generator acting as said compensation feedback impedance. In an embodiment, said first switching transistor has a gate terminal connected to said third circuit node and said second switching transistor has a gate terminal connected to said switching internal circuit node and thus to said second inverter of said startup detection block.

"In an embodiment, said auxiliary circuit is coupled between said first and second voltage references and is based on a same topology and on same types of components as said main circuit.

"In an embodiment, said main circuit is a low power and low quiescent current bandgap circuit and said auxiliary circuit is a high power functional copy thereof having an output voltage value being highly and correctly correlated to said one of the bandgap main circuit and a quiescent current much higher than the one of said main bandgap circuit.

"In an embodiment, a method for providing a startup correction to a main circuit connected to a startup circuitry comprises the steps of: detecting a startup state of said main circuit; providing a correct output voltage value corresponding to a voltage value of said main circuit at the end of said startup state; opening a feedback loop of said main circuit; and applying said correct output voltage value to an output terminal till the end of said startup state of said main circuit.

"In an embodiment, said step of opening said feedback loop of said main circuit is performed by said startup circuitry which has a first circuit node connected to an output terminal of said main circuit and a second circuit node connected to its feedback terminal and comprises at least a switching block connected to an auxiliary circuit, which is a functional copy of said main circuit not suffering from the same startup variations, and to a startup detection block providing an enabling signal corresponding to a state of said main circuit wherein a startup is needed, said switching block being able to open said feedback loop.

"In an embodiment, said step of applying said correct output voltage value is performed by said auxiliary circuit.

"In an embodiment, the method further comprises a step of detecting the begin and the end of said startup state of said main circuit.

"In an embodiment, said step of detecting is performed by said startup detection block.

"In an embodiment, the method further comprises a step of disconnecting said correct output voltage value at the end of said startup state of said main circuit.

"In an embodiment, said step of disconnecting is performed by said switching block.

"In an embodiment, a device comprises: an input node configured to couple to an output of a circuit having a feedback input; a feedback output node configured to couple to the feedback input of the circuit; and a startup module configured to detect a startup condition of the circuit, and when a startup condition is detected, break a connection between the output node of the circuit and the feedback node of the circuit and provide a feedback output signal to the feedback node of the circuit. In an embodiment, when a startup condition is detected the startup module is further configured to couple the feedback output node to an output node of the device. In an embodiment, when a startup condition is not detected the startup module is configured to couple the output of the circuit to the feedback input of the circuit and to the output node of the device. In an embodiment, the device further comprises an auxiliary circuit which is a functional copy of said circuit and wherein the startup module is configured to couple an output of the auxiliary circuit to the feedback input of the circuit and to the output of the device. In an embodiment, the startup module is coupled to a sensing terminal of said circuit and is configured to provide an enabling signal corresponding to a state of said circuit wherein a startup condition is detected. In an embodiment, the startup module comprises a switching block which is configured to couple between the output of the circuit and the feedback input of the circuit and is configured to couple to the output of said auxiliary circuit as well to said enabling signal, the switching block being configured to use the enabling signal as a driving signal to break the connection between the output of the circuit and the feedback input of the circuit. In an embodiment, the device further comprises a compensation feedback impedance, wherein the switching block is configured to couple the output of the circuit to a first reference voltage through the compensation feedback impedance when the startup condition is detected. In an embodiment, said switching block comprises a first and a second switch, both driven by said enabling signal, wherein: said first switch is configured to couple the output of the circuit to the compensation feedback impedance in a first operational state of the circuit, and to coupled the output of the circuit to the feedback input of the circuit in a second operational phase of said circuit, when a feedback loop of the circuit is to be closed; and said second switch is configured to coupled between the output of the auxiliary circuit the feedback input of the circuit and is closed in said first operational state of the main circuit, and is open in said second operational phase of said circuit, when said feedback loop is to be closed. In an embodiment, said auxiliary circuit is disconnected from a second voltage reference, in said second operational phase of said circuit, when said feedback loop is closed. In an embodiment, said circuit comprises at least an output driver transistor which is coupled between said second voltage reference and said output of the circuit and has a gate terminal connected to an internal circuit node of the circuit and wherein the startup module is coupled between said first and second voltage references and in turn includes at least a detection transistor which is coupled between said second voltage reference and a detection condenser, in turn connected to said first voltage reference interconnected in correspondence with a detection node, said detection transistor having a gate terminal connected to said internal circuit node. In an embodiment, said startup module further comprises a first and a second inverter which are inserted, in series to each other, between said detection node and a switching internal circuit node and configured to provide the enabling signal at an interconnection between the first and second inverters. In an embodiment, the switching block includes at least a first switching transistor being coupled, in series with a first current generator, between said output of the circuit and said first voltage reference as well as a second switching transistor being also coupled in series with a second current generator, between said output of the circuit and said first voltage reference, said first current generator acting as said compensation feedback impedance. In an embodiment, said first switching transistor has a gate terminal connected to said enable signal and said second switching transistor has a gate terminal connected to said switching internal circuit node and thus to said second inverter of said startup detection block. In an embodiment, said circuit and said auxiliary circuit are coupled between first and second voltage references and the auxiliary circuit is based on a same topology and on same types of components as said circuit. In an embodiment, said circuit is a low power and low quiescent current bandgap main circuit and said auxiliary circuit is a high power copy thereof having an output voltage value being highly correlated to said output of the bandgap main circuit and a quiescent current much higher than the quiescent current of said bandgap main circuit.

"In an embodiment, a method comprises: detecting a startup state of a main circuit; generating a startup output voltage value corresponding to a voltage value of said main circuit at the end of said startup state; opening a feedback loop of said main circuit; and applying said startup output voltage value to an output terminal until an end of said startup state of said main circuit. In an embodiment, said step of opening said feedback loop of said main circuit is performed by startup circuitry which has a first circuit node connected to an output terminal of said main circuit and a second circuit node connected to a feedback terminal of the main circuit and the startup circuitry comprises at least a switching block connected to an auxiliary circuit, which is a copy of said main circuit not suffering from a same startup variations as the main circuit, and to a startup detection block providing an enabling signal corresponding to a state of said main circuit wherein a startup is needed, said switching block configured to open said feedback loop. In an embodiment, said step of generating said startup output voltage value is performed by said auxiliary circuit. In an embodiment, the method further comprises a step of detecting a begin and the end of said startup state of said main circuit. In an embodiment, said step of detecting is performed by said startup detection block. In an embodiment, the method further comprises a step of disconnecting said startup output voltage value at the end of said startup state of said main circuit. In an embodiment, said step of disconnecting is performed by said switching block.

"In an embodiment, a system comprises: a circuit configured to generate an output signal provided to an output node and having a feedback loop; means for detecting a startup state of the circuit; means for responding to detection of a startup state by interrupting the feedback loop and coupling an alternative output signal to the output node. In an embodiment, the system further comprises means for generating the alternative output signal. In an embodiment, the circuit is configured to operate at a first power level and the means for generating the alternative output signal is a circuit having a similar structure as the circuit configured to generate the output signal and is configured to operate at a second power level higher than the first power level. In an embodiment, the circuit configured to generate the output signal is a low power and low quiescent current bandgap main circuit and the means for generating the alternative output signal is a higher power copy thereof configured to generate a stable alternative output signal in response to detection of a startup faster than the current bandgap main circuit.

"In an embodiment, an integrated circuit comprises: a first module configured to generate a first output signal and having a feedback input; a second module configured to generate a second output signal; and a startup module configured to: determine when the first module is in a startup mode; when the first module is in the startup mode, couple the second output signal to the feedback input of the first module; and when the first module is not in the startup mode, couple the first output signal to the feedback input of the first module. In an embodiment, the startup module is configured to: when the first module is in the startup mode, enable to second module and couple the second output signal to a node of the integrated circuit; and when the first module is not in the startup mode, disable the second module and couple the first output signal to the node of the integrated circuit. In an embodiment, the first module has a first configuration of components and is configured to draw power at a first power level and the second module has the first configuration of components and is configured to draw power at a second power level higher than the first power level.

"The characteristics and advantages of some embodiments of the startup circuitry and of the method will be apparent from the following description of an embodiment thereof given by way of indicative and non limiting example with reference to the annexed drawings."

For the URL and additional information on this patent, see: Schindler, Jaromir. Startup Circuitry and Corresponding Method for Providing a Startup Correction to a Main Circuit Connected to a Startup Circuitry. U.S. Patent Number 8324944, filed May 25, 2010, and issued December 4, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=59&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2933&f=G&l=50&co1=AND&d=PTXT&s1=20121204.PD.&OS=ISD/20121204&RS=ISD/20121204

Keywords for this news article include: STMicroelectronics Design and Application S.R.O.

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