Difference between revisions of "Modulation Plugin"
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*http://focus.ti.com/docs/prod/folders/print/ts5a1066.html | *http://focus.ti.com/docs/prod/folders/print/ts5a1066.html | ||
*call sample | *call sample | ||
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− | + | | [http://focus.ti.com/lit/ds/symlink/sn74lvc1g66.pdf SN74LVC1G66YZPR] || 1.65V~5.5V || -0.5V || 6.5V || 175MHz(3V) >300MHz(3V) (*1) | |
− | + | | 0.8ns(3.3V)||-40<sup>o</sup>C || 85<sup>o</sup>C || 6-pin || 1:$0.48 100:$0.27 | |
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− | | [http:// | + | | [http://focus.ti.com/lit/ds/symlink/sn74ahc4066.pdf SN74AHC4066DR] || 2V~5V || -0.5V || 7V || 30MHz(3V) |
− | | -40<sup>o</sup>C || | + | | 0.8ns(3.3V)||-40<sup>o</sup>C || 85<sup>o</sup>C || 14-pin || 1:$0.55 100:$0.33 |
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+ | (*1) different value of the RC circuit. ref. to the datasheet | ||
+ | more information about the series 74 in wiki: http://en.wikipedia.org/wiki/7400_series | ||
===op-amp buffer=== | ===op-amp buffer=== |
Revision as of 03:06, 9 July 2008
Contents
ToDos
- make sure each components freq. response, to make sure the highest freq.
- place DAC into this module board together, then only 4 wires(Vcc, I2C clk, Gnd & I2C data) from host.
- understand all components
- call sample
- draw circuit and PCB and grounding problem
- test by real circuit and firmware
Objectives
- The modulation module is used to deliver a digital output signal with the following characteristics:
- Square wave
- Variable frequency (>1kHz)
- Variable amplitude (0V - 2.5V)
- interface to MCU which do the control
Q: Is square wave where the "Lo" time is always at "GND" OK?
Q: If not, is a switch between "Lo is GND" vs. "Lo is negative Hi" OK? Or does "Lo" need to be independently controlled with another ADC?
Q: Will people be connecting a speaker directly to the output, requiring a relatively high-power output op amp such as the LM386N-3 ?
Software Solution
- Timer Interrupt controlling I2C 10-bit DAC can only achieve frequency response of about 1kHz
- 5byte/cmd
- 8bit/byte
- baudrate = 400kHz
- This yields 10kHz (0.1ms)
- As OS context switch is 10ms, set timer to 1ms (1kHz), so that 0.9ms can be used to process other tasks
- Due to higher freq. response requirement, so using hardware to implement the clock
Hardware Solution
Circuit
+-----+ +--------+ +--------+ I2C Bus | | | Analog | | Op-Amp | ------------+-----| DAC |------------| Switch |---------| |---------Output | | | +--------+ +--------+ | +-----+ | | | | +--------------+ | | | Programmable | | +-----| Clock |-------+ +--------------+
This architecture allows the square wave to run at a very high frequency, even with a slow I2C and a slow DAC.
Circuit Simulation by Paul Falstad's Web
- Import the following
$ 1 5.0E-6 16.817414165184545 64 5.0 50 w 128 256 144 256 0 w 16 256 64 256 0 g 16 352 16 368 0 v 64 64 112 64 0 0 40.0 2.5 0.0 0.0 0.5 w 112 128 144 128 0 w 64 128 16 128 0 w 16 128 16 256 0 v 64 256 128 256 0 2 1000.0 1.65 1.65 0.0 0.5 a 336 144 464 144 1 3.3 0.0 w 336 160 336 192 0 w 464 192 464 144 0 w 464 144 512 144 0 r 592 144 592 256 0 1000.0 g 592 352 592 368 0 w 512 144 592 144 0 w 336 192 352 192 0 w 432 192 464 192 0 v 64 128 112 128 0 1 1.0 1.25 1.25 0.0 0.5 w 16 256 16 288 0 w 16 288 16 352 0 w 592 256 592 352 0 g 272 352 272 368 0 w 272 128 336 128 0 w 176 256 176 144 0 r 272 224 272 288 0 1000.0 w 272 128 272 224 0 w 272 288 272 352 0 159 144 128 208 128 0 r 208 128 256 128 0 1000.0 w 256 128 272 128 0 w 144 256 176 256 0 r 336 224 336 288 0 1000.0 g 336 352 336 368 0 w 336 288 336 352 0 w 336 192 336 224 0 r 352 192 432 192 0 1000.0 o 4 64 0 34 2.5 7.8125E-4 0 -1 o 0 64 0 35 5.0 9.765625E-5 1 -1 o 11 64 0 34 2.5 0.0015625 2 -1
Components Inside Circuit
DAC chip
- datasheet -- http://focus.ti.com/lit/ds/symlink/dac6574.pdf
clk chip
- datasheet -- http://focus.ti.com/docs/prod/folders/print/cdc706.html
- call sample first, later to buy at -- http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=296-21381-5-ND
analog switch
Part No. | Operating Voltage | Min Volt | Max Volt | Frequency response | Propagation delay | Min Temp | Max Temp | Pin | Price(U.S.) |
---|---|---|---|---|---|---|---|---|---|
SN74LVC1G66YZPR | 1.65V~5.5V | -0.5V | 6.5V | 175MHz(3V) >300MHz(3V) (*1) | 0.8ns(3.3V) | -40oC | 85oC | 6-pin | 1:$0.48 100:$0.27 |
SN74AHC4066DR | 2V~5V | -0.5V | 7V | 30MHz(3V) | 0.8ns(3.3V) | -40oC | 85oC | 14-pin | 1:$0.55 100:$0.33 |
(*1) different value of the RC circuit. ref. to the datasheet
more information about the series 74 in wiki: http://en.wikipedia.org/wiki/7400_series
op-amp buffer
- OPA340