CN101227172B - Simulated D class amplifier - Google Patents
Simulated D class amplifier Download PDFInfo
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- CN101227172B CN101227172B CN2007100364667A CN200710036466A CN101227172B CN 101227172 B CN101227172 B CN 101227172B CN 2007100364667 A CN2007100364667 A CN 2007100364667A CN 200710036466 A CN200710036466 A CN 200710036466A CN 101227172 B CN101227172 B CN 101227172B
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Abstract
The invention discloses a simulating D amplifier, which comprises a transformation circuit for inputting signals-PWM wave, a driving circuit and an LC filtering circuit, wherein the transformation circuit for inputting signals-PWM wave comprises at least one amplifier and a phase-shift network, the phase-shift network is formed by a plurality of RC circuits and generates phase shift in a switch frequency range of the D amplifier, and phase shift is determined by the phase-shift value of the driving circuit and the connecting relation of the phase-shift network and the amplifier together, and a loop gain of the amplifier should be larger than a fixed start-oscillation constant. The simulating D amplifier preserves the advantages of low noise, low infidelity and the like of the existing D amplifier, and simultaneously has simpler structure and lower cost.
Description
Technical field
The present invention relates to a kind of D class A amplifier A, particularly relate to a kind of simulated D class amplifier, may be used on D analoglike power amplifier, especially the audio frequency amplification sector.
Background technology
The D class A amplifier A is obtaining more and more wider application because its high-efficiency characteristics, and especially at audio area, it amplifies after can the input signal (like audio signal) of lower frequency being transformed to the switch level of upper frequency (like hundreds of KHzs).Switch level after the amplification obtains the input signal that is exaggerated behind LPF.The part of D class A amplifier A most critical is for being changed to input signal the method for switch level.The switch level that the above-mentioned D of being used for class is amplified (below be called the PWM ripple) is characterized in that the low frequency component of PWM ripple frequency spectrum is consistent with input signal.Any PWM ripple with this characteristic can restore original input signal after the filtering, and therefore, the conversion from input signal to the PWM ripple is not unique.
At present, most widely used in the D class A amplifier A is the triangular wave comparison techniques.The triangular wave (or sawtooth waveforms) that this technology is used an outside input and input signal relatively, thereby produce a PWM ripple with the triangular wave same frequency.This technological essential characteristic is: the triangular wave (or sawtooth waveforms) that comprises outside input; Comprise a comparator unit, be used for the amplitude of comparison triangular wave and input signal.Delta-sigma is another kind of common technology, and this technology quantizes input signal integration (being the sigma operation) back, and the signal back input after the quantification subtracts each other (being the delta operation) with input signal.Signal after the above-mentioned quantification promptly is the PWM ripple that can be amplified to output.This technological essential characteristic is, comprises an integral unit, a quantifying unit, the feedback from quantifying unit output signal to the integral unit input signal.But above D class A amplifier A technical pattern is complicated, and required primary element sum is more, and cost is also higher.
Wen-bridge oscillator (wien ' s oscillator) is the general name of the RC oscillator of a type, and common have four kinds on integration phase shift oscillator, derivative-type phase shift oscillator, Wien bridge oscillator and a lead-lag oscillator, and their topological structure is as shown in Figure 1.Also have some similar RC oscillators to be also referred to as wen-bridge oscillator or other title, basically from these 4 kinds of oscillator distortion.As can beappreciated from fig. 1, their structure is made up of amplifier and phase-shift network.Big difference is the end points difference that feedback network connects, and the phase-shift network of integration phase shift oscillator and derivative-type phase shift vibration is connected in the negative feedback loop, and the phase-shift network of Wien bridge oscillator and lead-lag oscillator is connected in the positive feedback loop.Little difference is to realize that the method for phase shift is different, and the phase-shift network of integral form phase shift vibration adopts the phase shift of RC hysteresis formula, and the phase-shift network of differential phase shift oscillator adopts the phase shift of RC look ahead system.The phase-shift network of Wien bridge oscillator and lead-lag oscillator is existing to have hysteresis in advance again.But industry does not consider how to utilize wen-bridge oscillator through the proper parameters adjustment, to constitute one type of new D class A amplifier A as yet.
Summary of the invention
The technical problem that the present invention will solve provides a kind of simulated D class amplifier, when having kept advantages such as existing D class A amplifier A low noise, low distortion, has simpler structure, more less cost.
For solving the problems of the technologies described above; The present invention proposes a kind of simulated D class amplifier; Comprise an input signal-PWM ripple change-over circuit, a drive circuit and a LC filter circuit; Wherein: input signal-PWM ripple change-over circuit is used for converting input signal into the output signal, has promptly comprised the PWM ripple of frequency input signal composition, and this output signal is admitted to the input of drive circuit; Drive circuit receives the PWM ripple, and the PWM ripple after output is amplified gets into the LC filter circuit and feeds back to said PWM ripple change-over circuit simultaneously; The LC filter circuit receives the PWM ripple after amplifying, the output signal after output is amplified.Above-mentioned input signal-PWM ripple change-over circuit; Comprise: at least one amplifier and a phase-shift network; And phase-shift network one termination is received the PWM ripple after the amplification of output of drive circuit, and the in-phase input end or the inverting input of amplifier are promptly sent in the other end and input signal addition; Above-mentioned phase-shift network; Constitute by several RC circuit; And in the switching frequency scope of D class A amplifier A, produce phase shift, and phase shift determines by the phase-shift value of said drive circuit and the annexation of phase-shift network and amplifier jointly, that is: when the phase shift of drive circuit be 0 when spending; If stating phase-shift network links to each other with the in-phase input end of said amplifier, then phase shift is 0 degree; If phase-shift network links to each other with said amplifier's inverting input, then phase shift is positive 180 degree or negative 180 degree; When the phase shift of drive circuit is 180 when spending, if phase-shift network links to each other with the in-phase input end of amplifier, then phase shift is that positive 180 degree or negative 180 are spent; If phase-shift network links to each other with said amplifier's inverting input, then phase shift is 0 degree; The loop gain of above-mentioned amplifier should be greater than fixing starting of oscillation constant, that is: if the phase shift of said phase-shift network is positive and negative 180 degree, then loop gain should be greater than 29; If the phase shift of said phase-shift network is 0 degree, then loop gain should be greater than 3.
The present invention is owing to utilize existing oscillator (like Wen's oscillator); And it is carried out parameter adjustment, and after adding input signal, output meets the PWM ripple of D class A amplifier A requirement; This PWM ripple through drive circuit amplification, the filtering of LC filter circuit, can be constituted one type of new D class A amplifier A.
Description of drawings
Fig. 1 is the structural representation of wen-bridge oscillator;
Fig. 2 is four kinds of wen-bridge oscillators: the schematic circuit diagram of integration phase shift oscillator, derivative-type phase shift oscillator, Wien bridge oscillator and lead-lag oscillator;
Fig. 3 is the Phase-Shifting Characteristics sketch map of hysteresis formula RC circuit;
The input signal that Fig. 4 is based on Wien bridge oscillator changes PWM wave circuit figure;
Fig. 5 is the method sketch map that behind pierce circuit, adds drive circuit;
Fig. 6 is the structure chart of D class A amplifier A of the present invention;
It is the cut-away view of drive circuit module of the present invention that Fig. 7 gives;
Fig. 8 is the topological structure sketch map of 4 kinds of phase-shift networks;
Fig. 9 is the circuit diagram of a specific embodiment of the present invention;
Figure 10 is the effect curve figure of 20KHz sine wave after the output of Fig. 9 circuit.
Embodiment
Below in conjunction with accompanying drawing the present invention is done further detailed explanation.
At first tell about principle of the present invention: consider an oscillator, it will export the sine wave of a fixed frequency under the situation of not having input.If oscillating circuit is changed slightly, can the output signal be become the PWM ripple of fixed frequency.Because can regarding as, the nothing input is not input as zero, so this oscillating circuit has realized " zero input signal " is transformed to the method for PWM ripple in fact, at this moment, owing to input is fixing, so the pulsewidth of PWM ripple is also fixed.When the input signal non-zero, some oscillators (like crystal oscillator, bikini oscillator) can't be transformed to the PWM ripple that meets the requirement of D class A amplifier A with input signal; But other oscillators (like Wen's oscillator) are adjusted through proper parameters, and after adding input signal in position, output are met the PWM ripple of D class A amplifier A requirement.This PWM ripple through drive circuit amplification, the filtering of LC filter circuit, can be constituted one type of new D class A amplifier A.The content that this is proposed by the invention just.
As stated, some oscillator adds input signal in position after the proper parameters adjustment, can export the PWM ripple that meets the requirement of D class A amplifier A.But must point out that above-mentioned oscillator is the oscillator that meets property:
(1) must have metastable square wave oscillation frequency, be difficult for self-excitation;
(2) can change the duty ratio of square wave with extraneous triggering level;
(3) unintentional nonlinearity of oscillator own is little;
(4) the inner Amplifier Gain bandwidth product of oscillator should can work in hundreds of kilo hertzs or higher frequency to guarantee oscillator greater than 10,000,000.
Through test, the wien oscillator circuit satisfies above-mentioned requirements fully.Therefore, can be the basis, transform the D class A amplifier A with the wien oscillator circuit.
The target of above-mentioned parameter adjustment is:
(1) the adjustment feedback network makes oscillator that enough loop gains arranged.Loop gain when loop gain should guarantee much larger than the starting of oscillation of oscillator, so that oscillator works in the amplitude limit state, output is similar to the signal of square wave, and nonsinusoidal signal.Particularly, for integration phase shift oscillator, derivative-type phase shift oscillator, its loop gain should be much larger than 29; For Wien bridge oscillator and lead-lag oscillator, its loop gain should be much larger than 3.
(2) the adjustment phase-shift network vibrates oscillator and locates in the target switch frequency (like hundreds of KHzs) of D class A amplifier A.Particularly, for integration phase shift oscillator, derivative-type phase shift oscillator, should make phase-shift network phase shift 180 degree at target switch frequency place; For Wien bridge oscillator and lead-lag oscillator, the phase-shift network phase shift that should make target switch frequency place is 0 degree.
Because phase-shift network and feedback network are often overlapping, should carry out above-mentioned two adjustment repeatedly, above-mentioned two criterions of make suring all are satisfied.
The implantation site that adds of above-mentioned input signal is:
(1) for integration phase shift oscillator, derivative-type phase shift oscillator, input signal adds amplifier's inverting input,
(2) for Wien bridge oscillator and lead-lag oscillator, input signal adds the in-phase input end of amplifier.
After above-mentioned adjustment, (audio frequency) signal transformation that this circuit can will be imported is the PWM ripple, and the low frequency component of the frequency spectrum of this PWM ripple is consistent with input signal.This PWM ripple is sent into drive circuit amplify, again through the filtering of LC low pass filter, the input signal after can obtaining amplifying.Above-mentioned whole circuit promptly constitutes a D class A amplifier A.In practice,, often move behind the collection point with feedback signal, move to before the LC low pass filter by the inner amplifier out of oscillator for the error that drive circuit is brought also can be suppressed.Like this can be with the error of drive circuit by negative feedback inhibition.This adjustment process is as shown in Figure 5.Should carry out the oscillator parameter adjustment after the adjustment again, the adjustment criterion is consistent with above-mentioned criterion.Final D class A amplifier A structure is as shown in Figure 6.
Below in conjunction with accompanying drawing and specific embodiment the present invention is further explained.
Phase-shift network of the present invention all is to be made up of the RC circuit.These RC circuit or with phase lag, or phase place is leading, thus constituted various pierce circuit.Fig. 3 has illustrated the Phase-Shifting Characteristics of hysteresis formula RC phase-shift circuit.Wherein, Fig. 3 (a) is that a resistance and an electric capacity are formed first order pole RC circuit, and each limit can provide maximum-90 ° phase shift, like Fig. 3 (b).Such RC phase-shift network is claimed a joint RC circuit, the series connection of more piece RC circuit, and total phase shift angle is the phase shift summation of every joint.Phase place-the frequency characteristic that has shown 1～4 joint RC hysteresis phase-shift network at Fig. 3 (c).The look ahead system phase-shift circuit need only both can make the location swap of resistance and electric capacity the phase place of output signal be ahead of input signal.Phase place-the frequency characteristic figure of the phase place-frequency characteristic figure of look ahead system phase-shift network and hysteresis formula is similar, and just the ordinate with the latter's curve changes on the occasion of getting final product.One joint RC look ahead system phase-shift circuit has a zero point, and maximum+phase shift of 90 ° can be provided.Because pole and zero has the character opposite to even summation, thereby a limit and a series connection at zero point, it is zero that the phase shift that they produce will be offset.
Utilize above-mentioned characteristic, more piece RC circuit is combined, it is 0 degree or 360 degree that the loop that final circuit is located in target switch frequency (like, hundreds of KHzs) differs, and can constitute the phase-shift network circuit that meets requirement of the present invention.For example, phase-shift network is connected to reverse input end from output, the desirable phase shift of signalling channel is-180 degree; Feedback path is made up of 3 joint hysteresis RC phase-shift networks, every joint phase shift-60 degree, and three joint phase shifts are-180 degree altogether; The loop phase difference is 360 degree, thereby has guaranteed that circuit can vibrate.This phase-shift network is matched with an amplifier, can constitute the integration phase shift oscillator; This phase-shift network and an amplifier, drive circuit module are connected by aforementioned criteria with a LC filter circuit and adjust, and introduce input signal, can constitute a kind of realization of amplifier according to the invention according to aforementioned criteria.The distortion of phase-shift network has a variety of, and presents can't be enumerated one by one.But, promptly should think to meet the phase-shift network module of the present invention's statement as long as these distortion meet " it is 0 degree or 360 degree that the loop located in target switch frequency (like hundreds of KHzs) of final circuit differs ".For example, above-mentioned phase-shift network is become 4 joint retarded type RC by 3 joint retarded type RC, adjustment RC parameter makes the phase shift of its each joint at hundreds of KHzs place become 45 degree, promptly constitutes a kind of new phase-shift network.This phase-shift network is combined with an amplifier, promptly constitute the integration phase shift oscillator circuit of a distortion; This phase-shift network, amplifier, drive circuit, LC filter circuit are connected and adjustment by aforementioned criteria, and introduce input signal according to aforementioned criteria, the another kind that can constitute amplifier according to the invention is realized.Fig. 8 has enumerated 4 kinds of phase-shift network topology examples that can be used for circuit of the present invention, they also respectively with 4 kinds of wen-bridge oscillators shown in Fig. 2 in the phase-shift network structure corresponding.
Fig. 4 has illustrated to change the PWM wave circuit based on the input signal of Wien bridge oscillator.Wherein, the phase shift of phase-shift network (i.e. frequency-selective network shown in the figure) is 0 degree; Gate drive circuit, power MOS pipe (i.e. current switch shown in the figure) have all carried out operated in anti-phase respectively, so total phase shift of drive circuit is 0 degree.Therefore, as shown in the figure should phase-shift network being linked to each other with the in-phase input end of amplifier.Visible from figure, this circuit has only used an amplifier just to realize the conversion of input signal to the PWM ripple.Compare with delta-sigma structure (needing an integrator and a quantizer), triangular wave comparative structure circuit such as (needing a comparator and outside triangular wave input), structure is more simple.In addition, owing to this circuit itself is transformed based on oscillator, so it can export square wave (PWM ripple) when any input condition, do not need extra start-up circuit, thereby reduced the complexity of circuit.The index request of pair amplifier of the present invention is very low; Generally speaking; The amplifier of cut-off frequency more than 10 megahertzes can make circuit operate as normal of the present invention, such amplifier can use seldom the primary element of number (as, three transistors and some resistance) realize.Thereby circuit of the present invention is realized required overall primary element number seldom, not only is beneficial to monolithic integrated circuit and realizes, is more suitable in using discrete component to realize.In the high-power output fields of adopting discrete circuit to realize, the present invention has very strong competitive advantage more.
Fig. 5 has illustrated behind oscillator, to add the method for drive circuit.Fig. 5 a is the structural representation of wen-bridge oscillator.Wherein, arrow 1 is the output signal of oscillator, adjusting through aforementioned parameters, and to after the oscillator introducing input signal, this output signal is the PWM ripple that has comprised input signal information.This signal is sent in the drive circuit, the PWM ripple is amplified, can realize the function of D class A amplifier A.Arrow 2 has shown the feedback signal source of sending into phase-shift network.Can know by figure, in wen-bridge oscillator, send into the output signal of the signal of phase-shift network from oscillator.After adding drive circuit,, should make feedback signal change drive circuit output into by oscillator output signal for the error that drive circuit is introduced can be suppressed.Sketch map behind the adding drive circuit is shown in Fig. 5 b.
As shown in Figure 7, drive circuit module mainly is divided into two parts: gate drive circuit and power MOS pipe.The basic function of gate drive circuit is, receives the PWM ripple signal of oscillating circuit, and it is carried out level adjustment, shaping and amplification, make its become can the driving power metal-oxide-semiconductor pwm switching signal.Power MOS pipe carries out switch under the pwm switching signal control of gate drive circuit output, the PWM ripple after output is amplified is sent to the LC low pass filter.Gate drive circuit can adopt various structure to realize to the not influence of basic structure of oscillating circuit.For example, the function of gate drive circuit can be expanded according to the side circuit needs, as adding metal-oxide-semiconductor dead band controlled function etc.And for example, the structure of gate drive circuit not only can but also can be full bridge structure for half-bridge structure, when adopting full bridge structure, only need with after the PWM ripple signal inversion of oscillating circuit output through another group gate drive circuit, drive two groups of metal-oxide-semiconductors simultaneously and get final product.Fig. 8 has provided the circuit structure of a kind of semibridge system drive circuit that adopts in the reality, and this is a kind of but the structure that must stress driver module is not limited to shown in this circuit.
Fig. 9 is a specific embodiment of the present invention.Circuit uses the structure of Wien bridge oscillator as oscillating circuit among this embodiment, and drive circuit has adopted the semibridge system structure.T1～T4 forms a basic operational amplifier.The base stage of T2 is an amplifier's inverting input, and it is connected with the output of reverse current switch with R4 through R3, constitutes the gain negative feedback network, adjusts the loop gain that its resistance value will change D class A amplifier A feedback network.The base stage of T1 is the in-phase input end of amplifier, and audio signal is imported thus, with the duty ratio of control square wave, forms the PWM ripple of final output.
R1, C1, R2, C2 form phase-shift network, its acquired signal before the output low pass filter, and feed back to the base stage of T1.Adjust the phase shift that its resistance capacitance parameter value can change phase-shift network.
Above-mentioned partial circuit is accomplished square wave oscillation and voice modulation function, does not need power output, so only use in order to reduce power consumption ± the 5V power supply.
T5, T6, T7, T8 and D1, D2, D3, D4 form gate drive circuit jointly.Wherein, T7, T8 and D4 form half-bridge underarm nmos switch drive circuit, and the effect of Schottky diode D3 is in order to shorten T7 from time that saturation condition withdraws from.T5, T6 and D2 form half-bridge upper arm PMOS switch driving circuit, and operation principle is identical with following half-bridge, but operating state is just in time opposite with following half-bridge.
T9, T10 are half-bridge upper arm power MOS pipe, and T11 is a half-bridge underarm power MOS pipe.They are respectively according to the output of underarm on the gate drive circuit and switch.
The LC filter adopts 4 rank Butterworth LPF, to obtain filter effect preferably.
Figure 10 has provided the effect of 20KHz sine wave after foregoing circuit output.Wherein, the sine wave that amplitude is lower is an input signal, and the sine wave that amplitude is bigger is the signal after output passes through the amplification that obtains after the LC filter; The PWM ripple that square wave measures for the power MOS pipe place.
In sum; The invention discloses a kind of structure of simulated D class amplifier; Wherein: input signal-PWM ripple modular converter is realized by an improved wen-bridge oscillator; Be made up of an amplifier and a phase-shift network, it is changed the mechanism and relatively waits structure different with traditional delta-sigma structure, triangular wave; Drive circuit module is made up of gate drive circuit and power MOS pipe, and its structure has versatility widely, both can use half-bridge structure, also can use full bridge structure.Compare with existing D class A amplifier A, the present invention has simpler structure, and does not need start-up circuit to get final product steady operation when having kept advantages such as low noise, low distortion.Because its required primary element sum seldom, not only is suitable for using monolithic integrated circuit to realize, be more suitable in realizing this circuit with full discrete component, cost is 1/3rd of a common D class A amplifier A.
Claims (2)
1. simulated D class amplifier; Comprise an input signal-PWM ripple change-over circuit, a drive circuit and a LC filter circuit; Said input signal-PWM ripple change-over circuit comprises: at least one amplifier and a phase-shift network, and said phase-shift network one termination is received the PWM ripple after the amplification of output of said drive circuit; The in-phase input end or the inverting input of said amplifier are promptly sent in the other end and input signal addition; It is characterized in that:
Said phase-shift network is made up of several RC circuit, and in the switching frequency scope of D class A amplifier A, produces phase shift, and phase shift is determined by the phase-shift value of said drive circuit and the annexation of phase-shift network and amplifier jointly;
Said phase shift is meant by the common decision of the annexation of the phase-shift value of said drive circuit and phase-shift network and amplifier, and when the phase shift of drive circuit is 0 when spending, if said phase-shift network links to each other with the in-phase input end of said amplifier, then phase shift is 0 to spend; If said phase-shift network links to each other with said amplifier's inverting input, then phase shift is positive 180 degree or negative 180 degree; When the phase shift of drive circuit is 180 when spending, if said phase-shift network links to each other with the in-phase input end of said amplifier, then phase shift is that positive 180 degree or negative 180 are spent; If said phase-shift network links to each other with said amplifier's inverting input, then phase shift is 0 degree.
2. simulated D class amplifier as claimed in claim 1 is characterized in that: the loop gain of said amplifier should be greater than fixing starting of oscillation constant, that is: if the phase shift of said phase-shift network is positive and negative 180 degree, then loop gain should be greater than 29; If the phase shift of said phase-shift network is 0 degree, then loop gain should be greater than 3.
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| CN101227172B true CN101227172B (en) | 2012-05-30 |
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| CN104901680B (en) * | 2014-03-05 | 2019-01-08 | 北京兆易创新科技股份有限公司 | A kind of input/output interface device and chip system |
| CN110620623B (en) * | 2019-09-20 | 2021-07-27 | 深圳市智慧海洋科技有限公司 | Power amplifier and underwater acoustic communication equipment based on Class-D underwater acoustic communication |
| CN111884608A (en) * | 2020-08-03 | 2020-11-03 | 广芯电子技术（上海）股份有限公司 | Class D audio power amplifier and sampling triangular wave generating and filtering circuit used therein |
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| US4028633A (en) * | 1976-07-19 | 1977-06-07 | The United States Of America As Represented By The Secretary Of The Navy | Drive control to prevent simultaneous conduction in push-pull switching amplifier |
| CN1030013C (en) * | 1989-08-30 | 1995-10-11 | Gec阿尔斯托姆有限公司 | Feedback system control device and applications in amplifiers and servomechanisms |
| CN1110439A (en) * | 1993-11-23 | 1995-10-18 | 布拉德工艺公司 | An improved composite bridge amplifier with output overload and thermal protection |
| CN1525639A (en) * | 2003-02-26 | 2004-09-01 | 李相前 | A low distortion Class D amplifier |
| JP3561675B2 (en) * | 2000-03-29 | 2004-09-02 | 三洋電機株式会社 | Motor PWM drive circuit |
| CN1688179A (en) * | 2005-03-22 | 2005-10-26 | 东莞理工学院 | Feed back type active noise eliminating earpiece |
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2007
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Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4028633A (en) * | 1976-07-19 | 1977-06-07 | The United States Of America As Represented By The Secretary Of The Navy | Drive control to prevent simultaneous conduction in push-pull switching amplifier |
| CN1030013C (en) * | 1989-08-30 | 1995-10-11 | Gec阿尔斯托姆有限公司 | Feedback system control device and applications in amplifiers and servomechanisms |
| CN1110439A (en) * | 1993-11-23 | 1995-10-18 | 布拉德工艺公司 | An improved composite bridge amplifier with output overload and thermal protection |
| JP3561675B2 (en) * | 2000-03-29 | 2004-09-02 | 三洋電機株式会社 | Motor PWM drive circuit |
| CN1525639A (en) * | 2003-02-26 | 2004-09-01 | 李相前 | A low distortion Class D amplifier |
| CN1688179A (en) * | 2005-03-22 | 2005-10-26 | 东莞理工学院 | Feed back type active noise eliminating earpiece |
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