ABSTRACT. TAS half-bridges (6 single-ended [SE] channels)

Transcription

1 pplication Report LE047 February 00 Revised March 00 Power Rating in udio mplifiers uan Luu... Digital udio and Video Group BRC verage consumers often weigh heavily on cost versus power rating of audio amplifiers as their basis for purchasing one. Depending on the marketing strategy, the power rating methodology for audio amplifiers can vary from manufacturer to manufacturer. he purpose of this document is to clarify three commonly used power ratings: average power, peak power, and PMPO. he following exas Instruments PurePath Digital power stages will be used for power measurement: 4 4 half-bridges ( BL channels or 4 single-ended [E] channels) 4 half-bridges ( BL channels or 4 single-ended [E] channels) 86 6 half-bridges (6 single-ended [E] channels) Introduction. Power-Rating References and Basic Definitions here are a few standards that describe the power rating of an audio amplifier. he Federal rade Commission (FC) establishes fair advertisement practices for home audio power ratings. his is described in the FC document 63FR3733, 6 CFR, Chapter, Part 43. nother standard is the Electronic Industries ssociation (EI) E-0-. For the car audio industry, some manufacturers accept the Consumer Electronics ssociation CE-006- standard. It defines how the amplifier should be tested for power and signal distortion. How can one tell a good power rating from a bad one? For a good power rating, all the specified reference points are measurable. Ohm s law establishes the relationship of voltage, current and load, i.e., V = I R, where V = voltage, I = current in amperes and R = load resistance in ohms. Power is energy per time and is derived as P = V I = V /R = I R. For an audio signal, the voltage is in Vrms (root-mean-square), the power is referenced to a frequency of,000 Hz, and the load is usually referenced to a resistive load. hus, the power obtained is the average power that the amplifier can sustain. he FC requires further that the amplifier be pre-conditioned at one-eighth of rated total power output (for a multiple-output system, all channels are on) for one hour using a sinusoidal wave at a frequency of,000 Hz. he power spectrum measurement is then collected with two channels at maximum rated power over the audio frequency range of 0 to 0,000 Hz, in ambient still air of not less than C, for the duration of not less than minutes. ome manufacturers use an average power rating, but at a higher distortion ratio obtained by amplifying the original input signal to a level where clipping occurs. t 0% HD+N, the average power rating is higher than at % HD+N. For exas Instruments PurePath Digital power-stage data sheets, both unclipped and clipped power ratings are measured. PurePath Digital is a trademark of exas Instruments. ystem wo, udio Precision are trademarks of udio Precision, Inc. indows is a trademark of Microsoft Corporation. ll trademarks are the property of their respective owners. LE047 February 00 Revised March 00 Power Rating in udio mplifiers

2 est etup. Extended Power Ratings PMPO stands for peak music power output or peak momentary performance output. hese terms are used interchangeably and have approximately the same meaning. PMPO has no well-defined standard of measurement and is not generally used in high-fidelity audio as a performance measurement. In actuality, when manufacturers quote a PMPO number, it is often based on a theoretical calculation. PMPO power rating has no reference point. he power supply used for a class-b audio amplifier is much different than that for a digital audio amplifier (see Reference ). For a class-b audio power amplifier, PMPO can be quoted much higher than for a digital audio amplifier because of the physical properties of the analog components. he instantaneous voltage at start-up delivered by the power supply for a class-b audio power amplifier can be many times higher, thus producing a much higher power spike at start-up. PMPO is often quoted using this instantaneous start-up voltage. PMPO is a great marketing tool, because the customers are usually looking for a higher power rating with lower-cost audio amplifiers. Peak power ratings are obtained by using peak voltage. Peak power rating is sometimes referred to as music power. his music power is the dynamic headroom of the audio power amplifier which it can deliver when music transients occur. If the dynamic headroom of an audio amplifier is specified at 3 db, then the amplifier can deliver two times its average power; e.g., if the amplifier is rated for 00 average power, then the peak power is 400. For some high-end audio amplifiers, the dynamic headroom is lower because they have good power supplies that can deliver equally high power in any music dynamics. he following paragraphs define and derive two power ratings, namely, peak power and instantaneous peak power. hese two power ratings can be used as PMPO figures in cases where power ratings exceeding the standard rms power are needed in order to promote certain amplifier products in specific markets or regions. Both power ratings are measurable on actual hardware as opposed to more theoretically based PMPO definitions. est setups and test procedures are described and performed on three different exas Instruments power stages. For completeness, the rms power for the same power stages is also derived. he devices used as power stages in the following measurements are exas Instruments 4,, and 86. est etup Instruments: ystem wo -3 audio measurement system (P) by udio Precision Lab power supplies HP604, HPE360, HPE366, orensen DLM 60-0 Oscilloscope ektronix D784 Current probe ektronix CP0 Voltage probe ektronix P639 Loads DLE rated at 00, various resistance values Reference design boards DVREF63 and DVREF636 Instrument setup:. Power supplies are connected to the reference design board.. Resistive load is connected to the output of the power stage under test. 3. Current probe is connected to the output of the power stage under test. 4. Voltage probe is connected to the output of the power stage under test.. P is connected to the output of the power stage under test. Power Rating in udio mplifiers LE047 February 00 Revised March 00

3 Power Measurements udio Precision ystem wo 3 ektronix D784 V I nalog Input Load Resistance orensen DLM60 0 PV DD Outputs HPE 360 GV DD Device Under est HP 604 -V Digital upply I I C HPE 366 -V Digital upply I and I C Interface Board /PDIF Input GUI PC I C GUI I C Figure. est etup Block Diagram 3 Power Measurements 3. RM Power Description:. Use the typical operating voltage as specified in the data sheet for each device to set the voltage level for PV DD (MOFE voltage).. On the P, generate a -khz sine wave continuously at 0 dbf. 3. Use the typical resistive load as specified in the data sheet for each device. 4. et the modulator gain at 0 db.. et up the current probe to capture the output current waveform. 6. et up the voltage probe to capture the output voltage waveform. LE047 February 00 Revised March 00 Power Rating in udio mplifiers 3

4 Power Measurements Discussion: P RM V R I R he average power can be calculated from the power equation as previously described in the introduction section: Using parameters from the voltage or current trace captured by the oscilloscope (see the notes in able ): P RM I PP R, where I PP peak to peak current, R load resistance Note: he preceding equation applies to 0 db (unclipped) input. For clipped input (0% H+N), this equation does not apply. he result can be correlated with a power measurement captured using the P with the same exact test conditions. he P captures the Vrms value at the given load impedance using a high-precision meter. he values are then plotted using P indows software. ee the power vs frequency graphs in ppendix B. able. RM Power Unclipped DEVICE CONFIGURION CURREN (I pp ) LOD REINCE POER 4 86 BL () 3. 4 Ω 87 E () 7. 4 Ω BL (3) Ω 0 E (4) Ω 9. E satellite ().60 6 Ω 3. E subwoofer (6).04 3 Ω 4.7 () ee ppendix, Figure. For correlation with the P measurement, see ppendix B, Figure. () ee ppendix, Figure. For correlation with the P measurement, see ppendix B, Figure 3. (3) ee ppendix, Figure 3. For correlation with the P measurement, see ppendix B, Figure. (4) ee ppendix, Figure 4. For correlation with the P measurement, see ppendix B, Figure 7. () ee ppendix, Figure. For correlation with the P measurement, see ppendix B, Figure 9. (6) ee ppendix, Figure 6. For correlation with the P measurement, see ppendix B, Figure. exas Instruments (I) also provides RM power measurement with digital gain so that the HD+N is 0%. he digital gain is accomplished by using a I modulator, e.g., 08 or 086. he average power at 0% HD+N is higher than the normal FC-quoted power of <% HD+N. he following power table is the average power at 0% HD+N. ee ppendix B for the P power vs frequency graphs. able. RM Power at 0% HD+N DEVICE CONFIGURION verage Power at khz and 0% HD+N 4 86 BL () E () BL (3) E (4) E satellite () E subwoofer (6) () ee ppendix B, Figure. () ee ppendix B, Figure 4. (3) ee ppendix B, Figure 6. (4) ee ppendix B, Figure 8. () ee ppendix B, Figure 0. (6) ee ppendix B, Figure. 4 Power Rating in udio mplifiers LE047 February 00 Revised March 00

5 Power Measurements 3. Peak Power Description:. Use the typical operating voltage as specified in the data sheet for each device to set the voltage level for PV DD (MOFE voltage).. On the P, generate a -khz sine wave continuously at 0 dbf. 3. Use typical resistive loads as specified in the data sheet for each device. 4. et the modulator gain at 0 db.. et up the current probe to capture the output current waveform. 6. et up the voltage probe to capture the output voltage waveform. he peak power is measured at the peak of the current or voltage delivered into the load impedance. hus, deriving from the power equation we have peak power as follows: P PK V R I R Using parameters from voltage or current traces captured from oscilloscope (see the notes in able 3): P PK I PP R, where I PP peak to peak current, R load resistance able 3. Peak Power DEVICE CONFIGURION CURREN (I pp ) LOD REINCE POER 4 BL () 3. 4 Ω 74 E () 7. 4 Ω BL (3) Ω 03 E (4) Ω 9 86 E satellite ().60 6 Ω 47 E subwoofer (6).04 3 Ω 9 () ee ppendix, Figure. () ee ppendix, Figure. (3) ee ppendix, Figure 3. (4) ee ppendix, Figure 4. () ee ppendix, Figure. (6) ee ppendix, Figure 6. I does not publish the peak power for PurePath Digital power stages in the data sheets (see Conclusion, ection 4). he peak power can vary from system to system, and thus the system configuration limits the maximum peak power. 3.3 Instantaneous Peak Power Description:. Use the maximum operating voltage specified in the data sheet for each device to set the voltage level for PVDD (MOFE voltage), i.e., 4 = 34 V; = 37 V; 86 = 39 V.. On the P, generate -khz sine-wave bursts at 0 dbf. 3. Use various resistive loads in combination with the following step to determine the lowest resistance value before the device is shut down. 4. et the device for maximum digital gain without the device shutting down. his step is performed in combination with the previous step. he gain is adjusted until one complete sine wave is captured on the oscilloscope.. et up the current probe to capture the peak-to-peak current delivered into the load. 6. et up the voltage probe to capture the peak-to-peak voltage waveform. LE047 February 00 Revised March 00 Power Rating in udio mplifiers

6 Conclusion Discussion: he instantaneous peak power can be calculated using the parameters captured from the traces in ppendix C. able 4. Instantaneous Peak Power DEVICE CONFIGURION CURREN (I pp ) LOD REINCE Instantaneous Peak Power 4 86 BL (). Ω 38 E () 4. Ω 0 BL (3) 6.9 Ω 36 E (4) 4.8 Ω 4 E satellite () 0 3. Ω 88 E subwoofer (6). Ω 4 () ee ppendix C, Figure. () ee ppendix C, Figure. (3) ee ppendix C, Figure 3. (4) ee ppendix C, Figure 4. () ee ppendix C, Figure. (6) ee ppendix C, Figure 6. I does not publish the instantaneous peak power for PurePath Digital power stages in the data sheet (see Conclusion, ection 4). s mentioned in the introduction, the instantaneous peak power does not have any standard. he instantaneous peak power depends on the system and test setup configurations. 4 Conclusion exas Instruments (I) PurePath Digital audio devices deliver world-class performance. I always strives to maintain the highest standards and integrity in the products that are sold, including the supporting documentation, e.g., data sheets, application notes, etc. I power stages are tested using proper engineering techniques so that accurate measurements can be obtained (see Reference ). udio performance published in the data sheets is collected using P test equipment. his data, including the power rating, is traceable and reproducible using the I evaluation board (EVM). he power rating in the data sheet for each power stage is the average power that the device can deliver continuously. he need for attractive marketing strategies requires I customers to devise creative ways to use power rating for advertisements. his paper assists I customers in determining the suitable power rating to be used in the advertisement of their products. I supports customers internationally and understands that each region of the world requires different marketing strategies. hile the power rating for the U market is dictated by the FC, other countries may not be restricted to such requirements. In those cases, I customers are open to choose the acceptable power rating for advertisement. s mentioned in the introduction, PMPO generally is not well-defined and accepted as an audio performance measurement. It is used mostly for advertisements. he instantaneous measurement data detailed previously indicate the peak-to-peak current that a device can deliver to the specified load. hese data can be used for traceable and reproducible PMPO ratings for a given exas Instruments PurePath Digital application. References. Power upply Considerations for V Receivers (LE08). Digital udio Measurements (L4) FC 6 CFR, Chapter I, Part 43 6 Power Rating in udio mplifiers LE047 February 00 Revised March 00

7 ppendix ppendix Voltage and Current races. 4 Figure BL Figure E LE047 February 00 Revised March 00 Voltage and Current races 7

8 . Figure BL Figure E 8 Voltage and Current races LE047 February 00 Revised March 00

9 Figure E atellite Figure E ubwoofer LE047 February 00 Revised March 00 Voltage and Current races 9

10 ppendix B ppendix B udio Precision Power Graphs B. 4 exas Instruments, Inc. Power vs Frequency DVREF 636 (086 4BL) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain: 0 db; HD+N = KHz; Configuration : DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B BL exas Instruments, Inc. Power vs Frequency DVREF 636 (086 4BL) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain:.4 db; HD+N = KHz; verage Power= 08. ; Configuration: DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B BL (0% HD+N) 0 udio Precision Power Graphs LE047 February 00 Revised March 00

11 4 exas Instruments, Inc. Power vs Frequency DVREF 636 (086 4E) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain: 0 db; HD+N = KHz; Configuration: DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B E exas Instruments, Inc. Power vs Frequency DVREF 636 (086 4E) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain:.4 db; HD+N = KHz; verage Power= 3.6 ; Configuration: DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B E (0% HD+N) LE047 February 00 Revised March 00 udio Precision Power Graphs

12 B. exas Instruments, Inc. Power vs Frequency DVREF 636 (086 BL) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain: 0 db; HD+N = KHz; Configuration : DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B-. - BL exas Instruments, Inc. Power vs Frequency DVREF 636 (086 BL) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain:.4 db; HD+N = KHz; verage Power= 6.4 ; Configuration : DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B-6. - E (0% HD+N) udio Precision Power Graphs LE047 February 00 Revised March 00

13 exas Instruments, Inc. Power vs Frequency DVREF 636 (086 E) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain: 0 db; HD+N = KHz; Configuration : DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B-7. - BL exas Instruments, Inc. Power vs Frequency DVREF 636 (086 E) k k k 0k 0k HERZ PVDD 3 V; Load 4 Ohm; Gain:.4 db; HD+N = KHz; verage Power= 37.6 ; Configuration: DVREF636 79(.00) DVREF636 PR FRQ.atc Figure B-8. - E (0% HD+N) LE047 February 00 Revised March 00 udio Precision Power Graphs 3

14 86 B.3 86 exas Instruments, Inc. Power vs Frequency DVREF 63 (086 86E) atellite k k k 0k 0k HERZ PVDD 38 V; Load 6 Ohm; Gain: 0 db; HD+N = KHz; Configuration : DVREF63 79(.00) DVREF636 PR FRQ.atc Figure B E atellite exas Instruments, Inc. Power vs Frequency DVREF 63 (086 86E) atellite k k k 0k 0k HERZ PVDD 38 V; Load 6 Ohm; Gain:.4 db; HD+N = KHz; Configuration : DVREF63 79(.00) DVREF636 PR FRQ.atc Figure B E atellite (0% HD+N) 4 udio Precision Power Graphs LE047 February 00 Revised March 00

15 86 exas Instruments, Inc. Power vs Frequency DVREF 63 (086 86E) ubwoofer k k k 0k 0k HERZ PVDD 38 V; Load 3 Ohm; Gain: 0 db; HD+N = KHz; Configuration : DVREF63 79(.00) DVREF636 PR FRQ.atc Figure B E ubwoofer exas Instruments, Inc. Power vs Frequency DVREF 63 (086 86E) ubwoofer k k k 0k 0k HERZ PVDD 38 V; Load 3 Ohm; Gain:.4 db; HD+N = KHz; Configuration : DVREF63 79(.00) DVREF636 PR FRQ.atc Figure B E ubwoofer (0% HD+N) LE047 February 00 Revised March 00 udio Precision Power Graphs

16 ppendix C ppendix C Instantaneous Voltage and Current races C. 4 Figure C BL Figure C E 6 Instantaneous Voltage and Current races LE047 February 00 Revised March 00

17 C. Figure C-3. - BL Figure C-4. - E LE047 February 00 Revised March 00 Instantaneous Voltage and Current races 7

18 86 C.3 86 Figure C E atellite Figure C E ubwoofer 8 Instantaneous Voltage and Current races LE047 February 00 Revised March 00

19 IMPORN NOICE exas Instruments Incorporated and its subsidiaries (I) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. ll products are sold subject to I s terms and conditions of sale supplied at the time of order acknowledgment. I warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with I s standard warranty. esting and other quality control techniques are used to the extent I deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. I assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using I components. o minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. I does not warrant or represent that any license, either express or implied, is granted under any I patent right, copyright, mask work right, or other I intellectual property right relating to any combination, machine, or process in which I products or services are used. Information published by I regarding third-party products or services does not constitute a license from I to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from I under the patents or other intellectual property of I. Reproduction of information in I data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive business practice. I is not responsible or liable for such altered documentation. Resale of I products or services with statements different from or beyond the parameters stated by I for that product or service voids all express and any implied warranties for the associated I product or service and is an unfair and deceptive business practice. I is not responsible or liable for any such statements. Following are URLs where you can obtain information on other exas Instruments products and application solutions: Products pplications mplifiers amplifier.ti.com udio Data Converters dataconverter.ti.com utomotive DP dsp.ti.com Broadband Interface interface.ti.com Digital Control Logic logic.ti.com Military Power Mgmt power.ti.com Optical Networking Microcontrollers microcontroller.ti.com ecurity elephony Video & Imaging ireless Mailing ddress: exas Instruments Post Office Box 6303 Dallas, exas 76 Copyright 00, exas Instruments Incorporated