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very basic Class-D signal diagram. Figure 1. Class-D Power Amplifier Signal Diagram implemented in either analog or digital form. several blocks to condition the input signal before transferring to the output MOSFETs. without using many external components by directly driving the speaker using the high drive I/O. lower-cost, general-purpose development platform for the SiM3U1xx USB MCUs.
device should be as high as possible without causing saturation, which the red LED (DS8) indicates. ToolStick in Device Manager once it’s properly enumerated as a USB Audio device. settings for the device can be selected using the Properties button in this tab. Figure 3. Configuring the USB Utility Class-D ToolStick as the Playback or Recording Device ToolStick) as shown in Figure 4. When recording, the red LED (DS8) indicates when the microphone input saturates. Mixer or the recording program.
Figure 4. Selecting the USB Utility Class-D ToolStick in Volume Mixer In prerecorded flash mode, the Class-D ToolStick will output ~7 seconds of sound from an array saved to flash. Enter the mode by pressing the MODE button until blue LED DS3 turns on. MODE button until blue LED DS4 turns on. (DS8) indicates when the microphone input saturates. before it completes. The blue LED (DS6) will indicate when a play operation is in progress.
stereo jack and microphone gain/bias section of the board. The output network consists of a ferrite bead, LC, and grounding caps for each pair of channels, R+/R– and L+/L–. Output Network‚" on page 18. debug adapter can be used with the Precision32 (1.0.2 and higher) and ARM uVision IDEs (4.54 and higher). Table 2. Terminal Block Pin Descriptions (J4) Table 1. Class-D ToolStick Switches and LEDs (Continued)
slider in descending order from the location labeled MODE to the location labeled PLAY on the board. Table 3. Capacitive Sensing GPIO Connections
8 Rev. 0.1 5. Class-D ToolStick Firmware Overview 5.1. System Overview The system is configured for 48 MHz AHB and APB to maximize the output resolution of the EPCA. In all modes, the EPCA0 operates continuously and out puts the PWM signal to the speaker. This waveform generation is never interrupted. The SARADC modules operate in 12-bit mode at the maximum SAR clock frequency in order to complete conversions as quickly as possible . The USB internal oscillator provides the 48 MHz system clock, which in conjunction with the PLL0 module, provides the precise timing required in the different modes to recreate the audio waveforms. 5.1.1. SiM3U164 Module Usage The modules used by the Class-D ToolStick firmware are: SARADC0: Measures the right stereo jack channel and the microphone input SARADC1: Measures the left stereo jack channel VREF0: Provides the 2.4 V reference for the ADCs FLASHCTRL0: Writes recorded microphone data to flash EPCA0: Generates Class-D PWM waveforms (four channels) CAPSENSE0: Provides button and slider user interface TIMER0: Generates ~20 ms capacitive sensing scan timer TIMER1: Generates mode timing (e.g. 48 kHz in USB) and handles LED PWM updates PCA0 and Crossbar: Generates LED PWM waveforms for the six blue LEDs (one channel) USB0: Provides the USB Audio input/output interface PLL0: Provides the precise timing for the system and spectrum spreading to reduce emissions AppBuilder generates the initialization code for all modules except for the USB0 module. This AppBuilder project is included in the Utility Class-D ToolStick software package. Note: Exporting code from version 1.1.1 of AppBuilder will overwrite the project file associated with the Class-D ToolStick firm- ware. This project file includes manual changes to include the si32Library that will be removed when AppBuilder exports the code. A saved version of the project file ( save.project) is available in the Class-D ToolStick firmware package in case this project file is overwritten. To rest ore the project file, simp ly copy the contents of save.project to the .project file. 5.1.2. Firmware Organization The Class-D ToolStick code follows the AppBuilder code organization scheme. The application-specific code for each peripheral is in the src folder in the my- files, and the generated files from AppBuilder are in a generated folder below the src folder. Additional application-specific files are in the src folder with names associated with the functions in the file, like mulaw or LED_control. class_d: includes the main Class-D loop and any control not handled by the TIMER1L interrupt handler. LED_control: blue and red LED update functions; handles the shifting of the PCA channel on the crossbar. mulaw: implements the µLaw companding algorithms. myApplication: implements the system initialization code before passing control to class_d. myBuildOptions: required for si32Library. myDataPlaneIn: si32Library callback functions for the USB IN transactions (recording). myDataPlaneOut: si32Library callback functions for the USB OUT transactions (playing). myUsbAudioDevice: USB Audio descriptors and audio-specific si32Library function calls. myUSB0: non-audio USB si32Library functions calls for the application. pre_recorded_array: µLaw compressed prerecorded flash data. volume: handles the volume decoding and control from either the USB interface or the Capacitive Sensing slider. my- files: implement application code associated with the particular peripheral. g- files: AppBuilder generated initialization code associated with the particular peripheral.
and µLaw. This section also describes Remainder-Weighted Dithering as an optional algorithm. averaging to filter the ADC results. previous output and provide more smoothing. The EWMA is a form of IIR filter, which means it can become unstable if the cumulative error becomes too large. energy lost in the LSBs during this conversion in a random, inaudible way. positive and the LSBs are greater than the random valu e, then the LSB of the 9-bit data is incremented by 1. by 1. Otherwise, the data remains unchanged. Figure 6. Remainder-Weighted Dithering Example
not necessarily be the case in the operation of the algorithm. noticeable degradation in audio quality. compressed result as shown in Figure 7, where S is the sign bit. Finally, the 8-bit value is complemented. Figure 7. µLaw Algorithm Table Figure 8 shows the plot of the 14-bit signed inputs versus the 8-bit compressed output. Figure 8. µLaw Algorithm Plot
00000001 ABCD X
0000001 ABCD XX
000001 ABCD XXX
00001 ABCD XXXX
0001 ABCD XXXXX
001 ABCD XXXXXX
01 ABCD XXXXXXX
1 ABCD XXXXXXXX
000 ABCD
001 ABCD
010 ABCD
011 ABCD
100 ABCD
101 ABCD
110 ABCD
111 ABCD
build configuration are shown in Table 4. and select Build ConfigurationsSet ActiveDebug or Release. Figure 18. Setting the Active Precision32 IDE Build Configuration Table 4. Build Code Size Comparisons
- Tuning the Class-D Output Network
network shown in Figure 21 may provide better performance than the original configuration. Figure 20. Revision 1.0 Hardware Class-D Output Network—Direct Drive and the grounding capacitors provide additional filtering in conjunction with the speaker reactance. series components, if desired.
components should be tuned for the gate capacitance of the FETs. Figure 23. Full-Bridge Class-D Output Network—External MOSFETs
Figure 24. Utility Class-D ToolStick Board Schematic (1 of 3)—Revision 1.0
Figure 25. Utility Class-D ToolStick Board Schematic (2 of 3)—Revision 1.0
600 Ohm
Figure 26. Utility Class-D ToolStick Board Schematic (3 of 3)—Revision 1.0
Table 6. Utility Class-D ToolStick Board Bill of Materials
2397 SPC Technology STANDOFF HDW
Table 6. Utility Class-D ToolStick Board Bill of Materials (Continued)
Rev. 0.1 27 NOTES:
28 Rev. 0.1 CONTACT INFORMATION Silicon Laboratories Inc.
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