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HF-VFO using an AD9854
Craig Johnson, AAØZZ
Direct Digital Synthesizer
FDIM 2003May 15, 2003
AGENDA
1. Introduction
2. What Does A DDS Do?
3. Block Diagram
4. Hardware Description
5. Software Description
6. Results
7. HF-VFO with an R2Pro
8. Extensions
9. Concluding Remarks
10. Questions
FDIM 2003May 15, 2003
AAØZZ
Block Diagram
FDIM 2003May 15, 2003
AAØZZ
DDS
Clock
PIC
MainEncoderPIC
Encoder
LEDs
PushButtons
I out
Q out
LP
LP
Filter
Filter
Amp
Amp
Display
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word
AD9854 FTW = Desired Freq X ------------------ 248
Frequency (Hz)
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
AD9850 FTW = Desired Freq X ------------------ 232
Frequency (Hz)
Frequency Tuning Word
AD9854 FTW = Desired Freq X ------------------ 248
Frequency (Hz)
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
AD9850: 34
1 Hz 1 MHz
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
AD9850: 34 ~34 Million
1 Hz 1 MHz
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
AD9850: 34 34.359738 x 106
1 Hz 1 MHz
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
AD9854:
AD9850: 34 34.359738 x 106
1 Hz 1 MHz
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
AD9850: 34 34.359738 x 106
1 Hz 1 MHz
AD9854: ~2.25 x 106
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9854: ~2.25 x 106 ~2.25 x 1012
AD9850: 34 34.359738 x 106
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
- On each clock pulse the DDS performs calculations
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
based on: Frequency Tuning Word
- On each clock pulse the DDS performs calculations
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
based on: Frequency Tuning WordCurrent phase
- On each clock pulse the DDS performs calculations
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
based on: Frequency Tuning WordCurrent phase
- The DDS does look-up in sine table
- On each clock pulse the DDS performs calculations
What Does A DDS Do?
FDIM 2003May 15, 2003
AAØZZ
DDS01101011
Clock
DAC
FTW
based on: Frequency Tuning WordCurrent phase
- The D-to-A Converter (DAC) sets output voltages to desired levels
- On each clock pulse the DDS performs calculations
- The DDS does look-up in sine table
Quadrature
FDIM 2003May 15, 2003
AAØZZ
FDIM 2003May 15, 2003
AAØZZ
Block Diagram
DDS
Clock
PIC
MainEncoderPIC
Encoder
LEDs
PushButtons
I out
Q out
LP
LP
Filter
Filter
Amp
Amp
Display
Hardware Description• 2 PIC Microcontrollers
• AD9854 DDS
• 5-v Regulator
• 3.3-v Regulator
• 125 MHz Reference Clock
• Low Pass Filter (30 MHz)
• RF Amplifier (ERA-3 MMIC)
• Optical Encoder (or Mechanical)
• Pushbuttons, LEDs
• Display (LCD)FDIM 2003May 15, 2003
AAØZZ
Prototype – Front
FDIM 2003May 15, 2003
AAØZZ
Prototype – Back
FDIM 2003May 15, 2003
AAØZZ
Software Description
• Encoder PIC microcontroller
• Main PIC Microcontroller
• Display (LCD)
• Pushbuttons and LEDs
• Dual VFO (Split Operation)
• Calibrate
• AD9854 Initialization
FDIM 2003May 15, 2003
AAØZZ
Results• 2 Outputs – Quadrature (900)
• 2-v p-p (10 dBm) I and Q
• 0 - 30 MHz
• Used in R2Pro (Don Huff, W6JL)
- “It’s HOT!”
• 40 dB Opposite Sideband Rejection
-“40 dB sounds astonishingly good”
• Spurs?
- “Low” (need more measurements)
• Phase Noise?FDIM 2003May 15, 2003
AAØZZ
Prototype – Operational
FDIM 2003May 15, 2003
AAØZZ
Prototype – LCD
FDIM 2003May 15, 2003
AAØZZ
HF-VFO with an R2Pro Receiver
FDIM 2003May 15, 2003
AAØZZ
AudioFilters
AnalogSignal
ProcessorDownconverter
VFO
I Q
RFAmp
AudioAmp
Antenna
RF inSpeaker
(Rick Campbell, KK7B)
Early Prototype Running R2ProDon Huff, W6JL
FDIM 2003May 15, 2003
AAØZZ
Extensions
1. Add a Phase Lock Loop (PLL)
2. Upgrade the 125 MHz reference clock
3. Try different filter(s), amplifiers
4. Add a CW sidetone
5. Add Transmit/Receive keying delay logic for dual VFO operation
6. Change the 5-V Regulator
7. Add circuitry to change USB/LSB
8. Experiment with spread spectrum
FDIM 2003May 15, 2003
AAØZZ
Conclusion
• Stable, usable VFO - as is
• Ready for your extensions
• Learning tool
PIC microcontrollers
DDS
FDIM 2003May 15, 2003
AAØZZ
Questions?
FDIM 2003May 15, 2003
AAØZZ