17082 AMP Creating Class D Amplifiers with PIC MCUs and Analog

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2 Agenda Audio Amplifier Specs. Class A/B/AB/D overview Op Amp Based Design PIC16 Subwoofer Amp Design dspic33 Subwoofer Amp Design PIC24 Analog Peripheral Amp Design Summary 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 2

4 Power Average continuous power: Load (8ohm, 4ohm) Maximum THD+N Frequency Range Example: 100W average continuous power into 8Ω at less than 1%THD+N, from 20 to 20KHz 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 4

5 Frequency Response Amplitude of output over a frequency range for a constant amplitude input Example: +0,-0.4dB, 20Hz to 20KHz at 3dB below rated power 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 5

6 THD + N Specifying total harmonic distortion plus noise you must define Output level Test frequency Bandwidth % THD+N Example 1%THD+N, 1KHz at ½ rated power, 10KHz BW THD 100* H 2 1 H H H H H H H.. H 2 N 2 N 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 6

9 Phase Time offset in a cycle of periodic waveform Defined over a few frequencies Not an issue on single channel Important on multichannel 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 9

10 Signal To Noise Ratio Ratio of nominal output level to noise in db At max output it is called dynamic range Important to know reference level of signal 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 10

14 Efficiencies Linear amplifiers have efficiency draw backs Theoretical max efficiency on Class AB is 78% Practically seems to be in 50% region Ex. 50 watt amp throws out approx 25 watts of heat!!! 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 14

15 MCP6Hxx Op Amp Input Offset Voltage: ±0.7 mv (typical) Quiescent Current: 135 μa (typical) Common Mode Rejection Ratio: 100 db (typical) Power Supply Rejection Ratio: 102 db (typical) Rail-to-Rail Output Supply Voltage Range: - Single-Supply Operation: 3.5V to 16V - Dual-Supply Operation: ±1.75V to ±8V Gain Bandwidth Product: 1.2 MHz (typical) Slew Rate: 0.8V/μs (typical) Unity Gain Stable Extended Temperature Range: -40 C to +125 C No Phase Reversal 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 15

18 Audio Measurement Tools Diagnostic System for Sound Fields (DSSF) Software Frequency Response THD Real Time Analyzer Impulse Response Signal Generator Oscilloscope M-Audio External Sound Card 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 18

Test Setup Signal Generator PC Sound Card Dummy Load 2013

23 Lessons Learned Very simple to design and make Large bulk caps are required 470uF to 1000uF on each of the +/- power rails Input amplifier must be clean of noise, other wise it will be amplified 50/60Hz hum can be present, if so larger bulk caps or linear regulators 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 23

Class D Basics 2013 Microchip Technology

29 Single vs. Split Supply Split Supply ½ bridge need large caps to create virtual rail, power on pop when Full bridge no advantage Single Supply ½ bridge need large caps to create virtual rail, power on pop when charging caps Full bridge only need one rail 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 29

32 Low THD PIC16 SubWoofer Design Watt output Freq Response Hz. Use PIC16 with 10 bit ADC, 10 bit PWM Allow for open and closed loop operation 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 32

Class D PIC16 Block 2013 Microchip Technology

36 ISR ADC/PWM Code // *************************************************************************// // this routine is the interrupt service routine Timer 2 // // *************************************************************************// void interrupt Timer2ISR(void){ // check if its a timer 2 flag if(tmr2if == 1) TMR2IF = 0; CaptureADC(); UpdatePWM(input); // turn interrupt on again GIE = 1; } 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 36

39 Lessons Learned Just like class B it was easy via layout and components to amplify noise Separate rail for preamp, PIC ADC Ensure uF per rail Synchronize ADC with PWM Half bridge needs FB and big caps to ensure no bus pumping Closed loop troublesome because bus pumping also modulates DC offset of feedback circuit 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 39

42 Design Goals >30W 8 ohms Hz Frequency Response Closed loop design < 1% THD in B/W of interest Achieve transparent bass audio quality with peripherals available on the dspic33 devices 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 42

43 dspic33 Device Families dspic33 MC Device Family Motor Control PWM 10/12 bit ADC up to 1.1 MSPS dspic33fj16mc201 dspic33 GS Device Family High Speed PWM (2) 10-bit 2 MSPS ADCs dspic33fj16gs Microchip Technology Incorporated. All Rights Reserved AMP Slide 43

46 dspic33 Family High Speed SMPS PWM 1.04 nsec Duty Cycle and Dead Time resolution Up to 9 PWM generators Independent time base and duty cycle for each generator Fault and Current-limit inputs Leading edge Blanking Many operating modes for power supply applications 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 46

47 dspic33 Family SMPS ADC 10-bit Resolution, 2 Msps 4 Msps devices with two ADCs Up to 6 dedicated S/H circuits Dedicated conversion trigger for each analog input pair Optimized for fast feedback in power supply applications 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 47

Full Bridge Class D Block 2013 Microchip Technology

51 GS504 Configuration Operate GS504 from Pri PLL and FRC oscillator at 48 MHz Aux PLL used for HS PWM > 15 bits KHz (39321 counts) 16x oversample by ADC TMR2 trigger for AN0/1 and AN2/3 Signal input (AN2) Differential bridge output (AN0, AN1) MSPS throughput 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 51

52 GS504 Class D Flowchart ADC Interrupt (384 KHz) Set up Micro PWM / ADC Accumulate ADC Results Calculate LPF Y 16x? Update Feedback And Signal Input N Main Loop PWM Period? Y Calculate PID Set PWM Duty 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 52

53 GS504 ADC ISR void _ISRFAST _ADCP1Interrupt(void){ SampleCount++; if(samplecount > 15){ // Get input signal accumulated result SignalInput = SampleAccum2-8192; SampleAccum2 = (int)adcbuf2; } else{ } // Get accumulated output feedback results OutputFeedback = SampleAccum1; SampleAccum1 = ((int)adcbuf0 - (int)adcbuf1); SampleCount = 0; // Accumulate signal input and differential feedback SampleAccum1 += ((int)adcbuf0 - (int)adcbuf1); SampleAccum2 += (int)adcbuf2; // Clear ADC interrupt flag _ADCP1IF = 0; } 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 53

54 GS504 Main Loop void _ISR _PWMSpEventMatchInterrupt(void){ Flags.PWM = 1; _PSEMIF = 0; } while(1){ if(flags.pwm == 1){ SignalInput <<= 2; IIRCanonic( 1, &FilterOut, &SignalInput, &LowpassFilter); ControlLoop.Setpoint = FilterOut; ControlLoop.Feedback = OutputFeedback; CalcPI(&ControlLoop); PDC1 = PWM_HALF_DUTY + (int)controlloop.output; Flags.PWM = 0; } } 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 54

THD 0dB -12dB Measurements taken at 100Hz, 8 ohm load 2013

61 Lessons Learned Single supply and differential feedback helped closed loop operation High-speed PWM and 16x oversampling minimized quantization errors at low signal levels Need separate supply rails for gate drivers 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 61

63 PIC24 KM Series PIC24F XLP MCUs with cost effective Intelligent analog integration 12-bit ADC 8-bit DAC Operational Amplifiers (Op amps) 5V operation Supports 5V operation along with the 3V operation First PIC24F family with Configurable Logic Cell (CLC) User configurable real time logic control NEW Multiple Output Capture Compare PWM Optimal flexibility by combining timers, input capture and output compare/pwm Advanced 16bit PWM capabilities 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 63

66 What Else Can We Do Pressure Sensor Using a pressure to determine the position of the driver s cone and using that as feedback. Code will capture instantaneous pressure for a known cabinet and driver and use an algorithm to get position. The position value is then used as the negative feedback for the control loop. Pressure sensors seem to have a 1msec response time. So its possible to use them for subwoofer designs. Probably requires some calibration and characterization of cabinet and driver system Microchip Technology Incorporated. All Rights Reserved AMP Slide 66

67 What Else Can We Do Accelerometer Using an accelerometer to determine the position of the driver s cone and using that as feedback. Done digitally using code to do integration. Some accelerometers have about a 1KHz bandwidth, which again could be used for feedback. High Gain Servo Technology Patent Velodyne patents the world's first High Gain Servo-Controlled subwoofer lowering distortion to below 1%. The patent contains specifications for a sealed accelerometer Microchip Technology Incorporated. All Rights Reserved AMP Slide 67

Audio Precision 2700 Series Instrument 2013 Microchip

72 Summary We now understand amplifier specifications Various classes of amplifiers Understand a few different implementations of amplifiers using various PIC microcontrollers 2013 Microchip Technology Incorporated. All Rights Reserved AMP Slide 72

73 LEGAL NOTICE SOFTWARE: You may use Microchip software exclusively with Microchip products. Further, use of Microchip software is subject to the copyright notices, disclaimers, and any license terms accompanying such software, whether set forth at the install of each program or posted in a header or text file. Notwithstanding the above, certain components of software offered by Microchip and 3 rd parties may be covered by open source software licenses which include licenses that require that the distributor make the software available in source code format. To the extent required by such open source software licenses, the terms of such license will govern. NOTICE & DISCLAIMER: These materials and accompanying information (including, for example, any software, and references to 3 rd party companies and 3 rd party websites) are for informational purposes only and provided AS IS. Microchip assumes no responsibility for statements made by 3 rd party companies, or materials or information that such 3 rd parties may provide. MICROCHIP DISCLAIMS ALL WARRANTIES, WHETHER EXPRESS, IMPLIED, OR STATUTORY, INCLUDING ANY IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTABILITY, AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT WILL MICROCHIP BE LIABLE FOR ANY DIRECT OR INDIRECT, SPECIAL, PUNITIVE, INCIDENTAL, OR CONSEQUENTIAL LOSS, DAMAGE, COST, OR EXPENSE OF ANY KIND RELATED TO THESE MATERIALS OR ACCOMPANYING INFORMATION PROVIDED TO YOU BY MICROCHIP OR OTHER THIRD PARTIES, EVEN IF MICROCHIP HAS BEEN ADVISED OF THE POSSIBLITY OF SUCH DAMAGES OR THE DAMAGES ARE FORESEEABLE. TRADEMARKS: The Microchip name and logo, the Microchip logo, dspic, FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART, PIC 32 logo, rfpic, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MTP, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries. Analog-for-the-Digital Age, Application Maestro, BodyCom, chipkit, chipkit logo, CodeGuard, dspicdem, dspicdem.net, dspicworks, dsspeak, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, mtouch, Omniscient Code Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE, rflab, Select Mode, SQI, Serial Quad I/O, Total Endurance, TSHARC, UniWinDriver, WiperLock, ZENA and Z-Scale are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. GestIC and ULPP are registered trademarks of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in other countries. All other trademarks mentioned herein are property of their respective companies Microchip Technology Incorporated. All Rights Reserved AMP Slide 73

Overview of Charge Time Measurement Unit (CTMU)

Overview of Charge Time Measurement Unit (CTMU) 2008 Microchip Technology Incorporated. All Rights Reserved. An Overview of Charge Time Measurement Unit Slide 1 Welcome to the Overview of Charge Time Measurement