Modulation Plugin

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

Overall Performance

• I2C Baudrate:
• Output Voltage Range:
• Output Frequency Range:
• Number of channels:

Selected Chips

Part No.	Description	Order Chip	Call Sample
DAC6574IDGS	Quad-channel 10-bit I2C DAC	Digit Key	No need
CY2545???	Quad PLL I2C Programmable Clock Generator	HQEW	Try Contact Cypress
MC74VHC4053DT	Analog Multiplexers		Try Contact ON Semiconductor

CY2545 is out of stock in digikey, so there is no more information about it.

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

• Part No: DAC6574IDGS
• datasheet
• Resolution: 10-bit
• I2C clock Frequency: upto 3.4Mbps
• No of channels: 4
• Operating Voltage: 2.7 - 5.5V
• Temperature range: -40 - 105^oC

Clock Generator chip

• CY2545???
• datasheet
• buy at here
• I2C clock Frequency: upto 400kbps
• No of channels: 4
• Operating Voltage: 2.5V, 3.0V, 3.3V
• Temperature range: -40 - 85^oC

Comparison between Different Clock Generator Chips

Part No.	Opertating Volt	Operating Freq	Min Volt	Max Volt	output freq	Min Temp	Max Temp	Pin
CY2545	2.5V, 3.0V, 3.3V	400KHz	-0.5V	4.5V	3- 166 MHz	-40oC	85oC	24-pin

CLK 1-8 : frequency output
  CLK 3 : frequency selection (FS)
          (Function 2) cy2545 has 4 PLLs, each PLLs can be set 2 frequency, CLK 3 use to select the frequency
  CLK 6 : spread spectrum ON/OFF control input
          (Function 2) for synthesizing and modulating the frequency
Vdd_CLK_BX (X=1,2,3) control the output frquency of Blanck X (X=1,2,3) 

               +------------------+        
               |         |        |------CLK 1
               |         | Bank 1 |
               |         |        |------CLK 2
               |------------------|     
               |         |        |------CLK 3
               |         | Bank 2 |------CLK 4
               |         |        |------CLK 5
               |------------------|
               |         |        |------CLK 6
               |         | Bank 3 |------CLK 7
               |         |        |------CLK 8
               +------------------+
CLKIN/RST ---1. 2.5V/3.0V/3.3V external reference clock frequency
             2. Reset function POR :back to default condition / 
                       Clean Start : keep the programmed value
Xout        Crystal frequency output
Xin/EXCLKIN Crystal frequency input/ 1.8V external clock input

• Coding

 [Start Bit]->[7-bits devices]-->[R/W bit]-->[  Slave  ]-->[   8-bits     ]--> ..   
 [ address ]  [   address    ]   [       ]   [ CLK ACK ]   [memory address]   
 
 ..[ACK]-->[8-bits]-->[  8-bits    ]-->....[  8-bits    ]......until... [stop bit]
   [   ]   [ data ]   [data in MA+1]       [data in MA+n]               [        ]

Analog Switch

• Part No: MC74VHC4053
• datasheet
• Switching Frequency: 120MHz
• No of channels: 4
• Operating Voltage:
• Temperature range: -40 - 85^oC

Comparison between Different Analog Switches

Part No.	Operating Volt(V)	Freq Resp(Hz) at 3V	On-state Resist(Ω) at 3V	Min Volt(V)	Max Volt(V)	Min Temp	Max Temp	Indenpent Circuit	Voltage Supply Source	Pin
SN74AHC4066	Vcc : 2V~5.5V	35MHz	29Ω	Vcc : -0.5V	Vcc : 7V	-40oC	85oC	4	single	14
74HC4051D	Vcc : 2V~10V Vee : -10V~2V	Nil	80Ω	Vcc :-0.5V Vee : -11V	Vcc : 11V Vee : 2V	-40oC	85oC	4	Dual	16
MC74VHC4051	Vcc : 2V~6V Vee : -6V~0V	80MHz	80Ω	Vcc :-0.5V Vee :-7V	Vcc : 7V Vee : 5V	-40oC	85oC	4	Dual	16
MC74VHC4052	Vcc : 2V~6V Vee : -6V~0V	90MHz	90Ω	Vcc :-0.5V Vee :-7V	Vcc : 7V Vee : 5V	-40oC	85oC	4	Dual	16
MC74VHC4053	Vcc : 2V~6V Vee : -6V~0V	120MHz	90Ω	Vcc :-0.5V Vee :-7V	Vcc : 7V Vee : 5V	-40oC	85oC	4	Dual	16

• more information about the series 7400 in wiki: http://en.wikipedia.org/wiki/7400_series
• there is model G which is super high speeds at more than 1 GHz in 7400 family, however this model is very expensive.

op-amp buffer

• OPA340

Possibly Useful References

An open source waveform generator