WO2008089182A1 - Multi-stage amplifier with multiple sets of fixed and variable voltage rails - Google Patents
Multi-stage amplifier with multiple sets of fixed and variable voltage rails Download PDFInfo
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- WO2008089182A1 WO2008089182A1 PCT/US2008/051072 US2008051072W WO2008089182A1 WO 2008089182 A1 WO2008089182 A1 WO 2008089182A1 US 2008051072 W US2008051072 W US 2008051072W WO 2008089182 A1 WO2008089182 A1 WO 2008089182A1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
- H03F1/0216—Continuous control
- H03F1/0222—Continuous control by using a signal derived from the input signal
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
- H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
- H03F1/0211—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers with control of the supply voltage or current
- H03F1/0216—Continuous control
- H03F1/0222—Continuous control by using a signal derived from the input signal
- H03F1/0227—Continuous control by using a signal derived from the input signal using supply converters
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
- H03F3/187—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only in integrated circuits
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
- H03F3/45183—Long tailed pairs
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/03—Indexing scheme relating to amplifiers the amplifier being designed for audio applications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/351—Pulse width modulation being used in an amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/405—Indexing scheme relating to amplifiers the output amplifying stage of an amplifier comprising more than three power stages
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/408—Indexing scheme relating to amplifiers the output amplifying stage of an amplifier comprising three power stages
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/504—Indexing scheme relating to amplifiers the supply voltage or current being continuously controlled by a controlling signal, e.g. the controlling signal of a transistor implemented as variable resistor in a supply path for, an IC-block showed amplifier
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/516—Some amplifier stages of an amplifier use supply voltages of different value
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45138—Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/30—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor
- H03F3/3001—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor with field-effect transistors
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
Definitions
- the present invention relates in general to the field of signal processing, and more specifically to a system and method for processing signals with a multi-stage amplifier having multiple fixed and variable voltage rails.
- Many electronic devices utilize one or more amplifiers to amplify an electrical signal.
- a microphone utilizes transducers to convert sound waves into a corresponding electrical signal.
- An audio and/or video playback device reads stored data and converts the data into an electrical signal.
- the electrical signal often has insufficient power to drive an output device such as an audio speaker.
- An amplifier amplifies the smaller electrical signal to a level sufficient to drive the output device.
- Conventional amplifiers utilize a single set of voltage rails to supply voltage rails to a multi-stage amplifier.
- Figure 1 depicts a closed loop amplifier circuit 100.
- Resistors Rl and R2 provide a voltage divider for input voltage V INM , and resistor R2 provides feedback resistance between the output and inverting terminals of operational amplifier 102.
- Resistors R3 and R4 provide a voltage divider circuit between input voltage V I N P and reference voltage V re f.
- Operational- amplifier 102 drives the output voltage V ou t so that the input voltages at the inverting and noninverting terminals of operational-amplifier 102 are approximately equal.
- a power supply supplies power to operational-amplifier 102 via voltage rails V DD and Vss to allow operational- amplifier 102 to operate.
- a multi-stage amplifier includes multiple amplification stages.
- operational-amplifier 102 includes multiple amplification stages.
- Each amplification stage utilizes power supplied by a power supply to amplify an input signal.
- the power supply provides a set of voltage rails, such as V DD and Vss, to each amplification stage of the multi-stage amplifier.
- voltage rail V DD represents a higher voltage with respect to voltage rail Vss
- voltage rail Vss represents a negative voltage or ground.
- FIG. 2 depicts a signal processing system 200 with a conventional multistage amplifier 202.
- Signal source 208 provides analog input signal x(t), and signal source 208 can be any signal source such as a microphone or an audio and/or video device. Signal source 208 can also be any internal signal source within an integrated circuit.
- an output device such as speaker 210.
- a power supply 302 provides operating power to each of amplification stages 204 and 206 by providing voltage rails V DD and Vss to power supply nodes of amplification stages 204 and 206.
- Amplification stage 204 includes power supply nodes V DD IN and Vss IN to receive voltage supply rails V DD and Vss from power supply 302.
- Amplification stage 206 includes power supply nodes V DD OUT and Vss OUT to receive voltage supply rails V DD and Vss from power supply 302.
- each of amplification stages 204 and 206 has a unique set of power supply nodes to receive the set of voltage rails V DD and Vss
- the multistage amplifier 202 is supplied by only one set of voltage rails, i.e. voltage rails V DD and Vss.
- FIG. 3 depicts integrated circuit 304 connected to external power supply 302.
- Amplifier 202 is implemented, in this embodiment, as an integrated portion of integrated circuit 304.
- Power supply 302 is an external device that provides power to integrated circuit 304 through pads 306 and 308.
- Pad 306 receives the V DD voltage rail of power supply 302, and pad 308 receives the Vss voltage rail.
- Each of pads 306 and 308 has two conductive paths (310, 212) and (314, 316) connected to amplifier 202.
- the power supply nodes V DD IN and V DD OUT are distinctly labeled for purposes of identifying a specific path to amplifier 202, voltage rails V DD IN and V DD OUT are actually identical to each other.
- power supply nodes Vss IN and Vss OUT are distinctly labeled for purposes of identifying a specific path to amplifier 202, voltage rails Vss IN and Vss OUT are actually identical to each other.
- the voltage rails to amplification stage are set so that each amplification stage operates properly.
- proper operation includes providing sufficient bias voltages to transistors within the amplification stage for operation in a predetermined mode, such as in a saturation mode, and providing sufficient input signal headroom.
- Input signal headroom represents a difference between an input signal level and a maximum input signal level that can be accommodated while still allowing the amplification stage to operate. Unless otherwise indicated, "input signal headroom” is referred to herein as "headroom”.
- the voltage supply rails are fixed at specific voltage levels. During operation, input signals swing between minimum and maximum voltage levels. Thus, the efficiency of the amplifier decreases as the input signal decreases.
- a method of amplifying an input signal includes receiving an input signal with a multi-stage amplifier.
- the method also includes receiving a mixed set of voltage rails, wherein each amplification stage of the multi-stage amplifier receives a set of the voltage rails and at least one member of one set of the voltage rails is a variable voltage rail.
- the method further includes amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.
- a signal processing device includes a multi-stage amplifier.
- the amplifier includes a first amplification stage having an output node and first and second power supply nodes, wherein during operation the first and second power supply nodes of the first amplification stage are coupled to respective first and second voltage rails.
- the amplifier also includes a second amplification stage, coupled to the output node of the first amplification stage, having first and second power supply nodes, wherein during operation the first and second power supply nodes of the second amplification stage are respectively coupled to a variable voltage rail and to a third voltage rail, and the first voltage rail is greater than the variable voltage rail.
- a method of amplifying an input signal includes receiving first and second power supply voltages with a first amplification stage of a multi-stage amplifier. The method further includes receiving third and fourth power supply voltages with a second amplification stage of the multi-stage amplifier, wherein the first power supply voltage is greater than the third power supply voltage, the third power supply voltage varies over time during operation of the multi-stage amplifier and the first and third power supply voltages are more positive than respective second and fourth power supply voltages. The method also includes receiving an input signal with the multi-stage amplifier and amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.
- a signal processing system includes a first amplification stage, wherein during operation the first amplification stage receives a fixed supply voltage and a first variable supply voltage, and the fixed supply voltage is greater than the first variable supply voltage.
- the system also includes a second amplification stage, coupled to an output of the first amplification stage, wherein during operation the second amplification stage receives the fixed supply voltage and the variable supply voltage.
- the system further includes a third amplification stage, coupled to an output of the second amplification stage, wherein during operation the third amplification stage receives a second variable supply voltage and the first variable supply voltage, wherein the fixed supply voltage is greater than a maximum second variable supply voltage.
- Figure 1 (labeled prior art) depicts a closed amplifier circuit.
- Figure 2 (labeled prior art) depicts a multi-stage amplifier.
- Figure 3 (labeled prior art) depicts an integrated circuit with a multi-stage amplifier connected to an external power supply.
- Figure 4 depicts a multi-stage amplifier having a mixed set of voltage rails.
- Figure 5 depicts a multi-stage amplifier in an audio signal processing system.
- a signal processing system and method utilizes a multi-stage amplifier to amplify an input signal.
- the multi-stage amplifier uses a mixed set of voltage rails to improve the operating efficiency of at least one of the amplification stages while allowing other amplification stages to operate in a predetermined operating mode. Efficiency of at least one of the stages is improved by providing a different set of the amplifier stages is improved by utilizing at least one variable voltage rail supplied to an amplification stage of the multi-stage amplifier.
- the variable voltage rail varies in response to changes in an input signal voltage to the amplification stage.
- the multi-stage amplifier operates with mixed sets of voltage supply rails to allow amplification stage efficiency and provide adequate voltage to allow operation of all amplification stages. Accordingly, at least one amplification stage utilizes a variable voltage rail, and all amplification stages are supplied with a set of voltage rails that provides sufficient input signal headroom.
- the multi-stage amplifier includes at least first and second amplification stages.
- the two amplification stages have different supply voltage requirements.
- the signal processing system and method provide a first set of voltage rails, which can be variable or fixed, to the first amplification stage and at least one variable voltage rail to the second amplification stage.
- the multi-stage amplifier can operate more efficiently than a conventional multi-stage amplifier with a fixed set of voltage rails for each amplification stage and still maintain sufficient input signal headroom for all amplification stages.
- Patent Application Serial Nos. 11/610,498 and 11/611,069 (collectively referred to herein as the "Cirrus Applications") claim priority to U.S. Provisional Application No. 60/823,036 filed on 21 August 2006, and the Cirrus Applications are incorporated herein by reference in their entireties.
- FIG. 4 depicts a multi-stage amplifier 400 to amplify analog input signal x(t) and generate analog output signal y(t) using multiple sets of voltage rails.
- the multi-stage amplifier 400 has N+l serially connected amplification stages 402.0, 402.1, ..., 402. ⁇ , where N is an integer greater than or equal to two.
- Each of the amplification stages 402.0, 402.1, ..., 402. ⁇ receives two respective sets of voltage rails, ⁇ V DD _ 0 , V ss _o ⁇ , ⁇ VDD_I, V SS _I ⁇ , ... , ⁇ V D D_N, VSS_N ⁇ .
- each set of voltage rails is set to provide sufficient headroom for the voltage swing of each input signal to each amplification stage.
- Particular values of the voltage rails depend upon the actual configuration of each of amplification stages 402.0, 402.1, ..., 402.N and the full swing of each input signal to each amplification stage.
- all the positive voltage rails, except that positive voltage rail V DD _ N of the last amplification stage are equal and fixed, and the voltage rail V DD _ N of the last amplification stage is a variable voltage rail.
- At least one set of voltage rails is provided by a variable voltage supply, such as the charge pump power supply illustratively described in the Cirrus Applications.
- a variable voltage supply such as the charge pump power supply illustratively described in the Cirrus Applications.
- each variable voltage rail supplied by the variable voltage supply dynamically adjusts, in response to the voltage level of an input signal to the amplification stage. The adjustment reduces a difference between the voltage of the output signal and the voltage supplied to the amplification stage while providing sufficient output signal headroom. Thus, efficiency of the amplification stage stages is improved.
- Different amplification stages have different voltage supply requirements for providing sufficient headroom and operational efficiency.
- at least one of the amplification stages 402.0, 402.1, ..., 402.N has a greater voltage supply requirement to provide headroom for the input signal.
- an analog input signal x(t) has a voltage level of +V 1n .
- voltage rail V DD _O equals (+V 1n + V ov h).
- V ov h is an overhead voltage that allows the transistors of amplification stage 402.0 to operate in saturation mode when the voltage level of analog input signal x(t) equals +V 1n .
- voltage rail V DD _ N for amplification stage 402.N equals +V 1n .
- V DD _ O V DD N -
- FIG. 5 depicts a multi-stage amplifier 500, which is one embodiment of multi-stage amplifier 400.
- the multi-stage amplifier 500 is a class AB amplifier with a differential input amplification stage 502.0.
- amplification stage receives and amplifies a difference between input signals V SUMM and V SUMP - Amplification stage 502.1 then amplifies the output of amplification stage 502.0, and amplification stage 502.2 amplifies the dual output of amplification stage 502.1.
- Amplification stage 502.1 provides dual output signals X 2P (t) and X 2n (t).
- CMOS field effect transistor (FET) 504 and p-channel CMOS FET 506 of amplification stage 502.2 both operate in saturation mode during normal operation of multi-stage amplifier 500.
- Respective voltage levels of input signals X 2P (t) and X 2n (t) determine the current through the respective FETs 504 and 506.
- FETs 504 and 506 work together in accordance with the voltage levels of input signals X2 P (t) and X2 n (t) to generate an analog output signal y(t).
- One or more power supplies provide voltage rails VDD_O, VSS_O, VDD_1 , and Vss_i to respective multi-stage amplifiers 502.0, 502.1, and 502.2. At least one of the voltage rails is variable. For example, in at least one embodiment, voltage rail V DD _1 is variable to increase the efficiency of amplification stage 502.2. In at least one embodiment, voltage rail Vss_i is also variable.
- the first set of voltage rails, ⁇ V DD _O, VSS_O ⁇ , and the second set of voltage rails, ⁇ V DD _ I , V SS _ I ⁇ form an exemplary mixed set of voltage rails because the sets are not identical, although each set may have a common member.
- Voltage rails V DD _O, VSS_O, and V DD _ I , VSS_ I can be respectively fixed or variable voltage rails.
- fixed voltage rails maintain a relatively constant voltage over time.
- fixed voltage rails can slightly vary over time due to, for example, an environmental factor such as temperature, fixed voltage rails are not responsive to any input signal to any amplification stage of multi-stage amplifier 500 and are not otherwise intentionally varied during operation of multi-stage amplifier 500.
- amplification stages 502.0 and 502.1 have different circuitry than amplification stage 502.2. In at least one embodiment, amplification stages 502.0 and 502.1 operate properly with the same voltage supply rails V DD _ O and Vss_o- To allow amplification stages 502.0 and 502.1 to operate, e.g.
- voltage rail set ⁇ V DD _O, VSS_O ⁇ differs from the voltage rail set (V DD _ I , VSS_ I ⁇ when the input signals to respective amplification stages drops below a predetermined value.
- voltage rails V DD _O, VSS_O, and Vss_i are fixed, and voltage rail V DD _ I is variable.
- multi-stage amplifier 500 is part of an audio signal processing system.
- the multi-stage amplifier 500 provides the analog output signal y(t) to speaker 508.
- components 410 such as a low pass filter, post-process the analog output signal y(t) prior to reception by speaker 508.
- Figure 6 depicts a schematic of amplification stage 600, and amplification stage 600 represents one embodiment of amplification stage 502.0.
- Amplification stage 600 is a differential amplifier and, thus, amplifies a difference between the differential input signals VSU MM and VSU MP -
- a power supply provides voltage rails V DD _O and Vss_o to supply power to amplification stage 600.
- FET Ml is connected as a diode and FETs Ml and M2 have common drain and gate voltages.
- FETs M3 and M4 respectively connected to the sources of FETs Ml and M2, respectively receive input signals V SUMM and V SUMP as gate voltages.
- p-channel FETs M3 and M4 maintain a saturated state during operation of amplification stage 600.
- a bias voltage V BIAS at the gate of FET M5 biases FET M5.
- V DD _ O When voltage rail V DD _ O equals or exceeds a minimum voltage and voltage rail Vss_o is below a minimum voltage, amplification stage 600 operates properly and provides sufficient headroom for the voltage swings of input signals VSU MM and VSU MP •
- the minimum V DD _O voltage rail can be determined from the schematic of amplification stage 600.
- the drain-gate voltage of FET Ml is Vossat + V TH _ MI -
- each of FETs Ml, M2, M3, M4, and M5 has the same drain-source saturation voltage Vossat and the same threshold voltage Vm-
- a voltage at the source of FET M3 is VSU MM - (Vossat + V TH ).
- Voltage V x represents a voltage at the drain of FET M3.
- V x > VsUMM max " (VoSsat + VTH) + VoSsat [1]
- V x > VsUMM max " VlH [2]
- V x V DD _o - V DSs a t - V ⁇ H [3]
- amplification stage 600 is configured as part of an operational-amplifier with feedback to the inverting terminal, and, thus, V SUMP is approximately equal to V SUMM - From Equations [4] and [7], to maintain FETs Ml, M2, M3, and M4 in saturation and provide sufficient headroom for input signal V SUMM and V SUMP :
- V D ssat 0.100 V
- VsuMMmax +0.9 V
- VsuMMmm 0 V
- V TH 0.7 V
- VSU MM VSU MP
- V DD _O is greater than or equal to +1.0 V to provide sufficient headroom and allow amplification stage 600 to operate in saturation mode.
- Vss_o is less than or equal to -0.9 V to provide sufficient headroom and allow amplification stage 600 to operate in saturation mode.
- V DD _ I when input signal X 2P (t) is +0.9 V, V DD _ I can be +0.9 V and still provide sufficient headroom for input signal X 2P (t).
- V DD _ O when V SUMM is +0.9 V, V DD _ O should be greater than or equal to +1.0 V.
- amplification stage 502.0 and 502.1 operate properly with the same voltage supply rails V DD _ O and Vss_o- Thus, by providing different voltage rails VDD_O and VDD_I, e.g.
- amplification stages 502.0 and 502.1 can operate properly in saturation mode and provide sufficient headroom for input signal V SUMM
- amplification stage 502.2 can operate efficiently and provide sufficient headroom for input signal X 2P (t).
- amplification stages 502.0, 502.1, and 502.2 can utilize the same voltage rails Vss_o and Vss_i- (38)
- the multi-stage amplifier uses a mixed set of voltage rails to improve the operating efficiency of at least one of the amplification stages while allowing other amplification stages to operate in a predetermined operating mode.
- the signal processing systems including multi-stage amplifier 400, can be implemented using discrete, integrated, or a combination of discrete and integrated components.
- the multistage amplifier can be used in any signal processing system including audio signal processing systems and video signal processing systems.
Abstract
Description
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Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB0912435A GB2458081B8 (en) | 2007-01-19 | 2008-01-15 | Multi-stage amplifier with multiple sets of fixed and variable voltage rails |
CN200880002403.2A CN101584112B (en) | 2007-01-19 | 2008-01-15 | There is many groups and fix the casacade multi-amplifier with variable voltage rails |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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US88567307P | 2007-01-19 | 2007-01-19 | |
US60/885,673 | 2007-01-19 | ||
US11/694,348 US8362838B2 (en) | 2007-01-19 | 2007-03-30 | Multi-stage amplifier with multiple sets of fixed and variable voltage rails |
US11/694,348 | 2007-03-30 |
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Publication Number | Publication Date |
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WO2008089182A1 true WO2008089182A1 (en) | 2008-07-24 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/US2008/051072 WO2008089182A1 (en) | 2007-01-19 | 2008-01-15 | Multi-stage amplifier with multiple sets of fixed and variable voltage rails |
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US (1) | US8362838B2 (en) |
CN (1) | CN101584112B (en) |
GB (1) | GB2458081B8 (en) |
WO (1) | WO2008089182A1 (en) |
Cited By (1)
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WO2010048256A1 (en) * | 2008-10-21 | 2010-04-29 | Analog Devices, Inc. | Headphone amplifier circuit |
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Also Published As
Publication number | Publication date |
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GB2458081B8 (en) | 2012-08-08 |
GB2458081B (en) | 2012-06-20 |
US20080174372A1 (en) | 2008-07-24 |
CN101584112A (en) | 2009-11-18 |
GB0912435D0 (en) | 2009-08-26 |
US8362838B2 (en) | 2013-01-29 |
CN101584112B (en) | 2016-01-20 |
GB2458081A (en) | 2009-09-09 |
GB2458081A8 (en) | 2012-08-08 |
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