HF-VFO%20using%20an%20AD9854

1
HF-VFO using an AD9854
Direct Digital Synthesizer
Craig Johnson, AAØZZ
FDIM 2003
May 15, 2003
2

• AGENDA
• Introduction
• What Does A DDS Do?
• Block Diagram
• Hardware Description
• Software Description
• Results
• HF-VFO with an R2Pro
• Extensions
• Concluding Remarks
• Questions

AAØZZ
FDIM 2003
May 15, 2003
3
Block Diagram
LEDs
Clock
LP
Encoder
DDS
I out
Amp
Main
Filter
Encoder
PIC
PIC
LP
Q out
Amp
Filter
Push Buttons
Display
AAØZZ
FDIM 2003
May 15, 2003
4
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
AAØZZ
FDIM 2003
May 15, 2003
5
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word
AAØZZ
FDIM 2003
May 15, 2003
6
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word
248
AD9854 FTW Desired Freq X
------------------
Frequency (Hz)
AAØZZ
FDIM 2003
May 15, 2003
7
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word
248
AD9854 FTW Desired Freq X
------------------
Frequency (Hz)
232
AD9850 FTW Desired Freq X
------------------
Frequency (Hz)
AAØZZ
FDIM 2003
May 15, 2003
8
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
AAØZZ
FDIM 2003
May 15, 2003
9
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AAØZZ
FDIM 2003
May 15, 2003
10
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34
AAØZZ
FDIM 2003
May 15, 2003
11
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34 34
Million
AAØZZ
FDIM 2003
May 15, 2003
12
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34 34.359738
x 106
AAØZZ
FDIM 2003
May 15, 2003
13
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34 34.359738
x 106
AD9854
AAØZZ
FDIM 2003
May 15, 2003
14
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34 34.359738
x 106
AD9854 2.25 x 106
AAØZZ
FDIM 2003
May 15, 2003
15
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
Frequency Tuning Word Examples (125 MHz Clock)
1 Hz 1 MHz
AD9850 34 34.359738
x 106
AD9854 2.25 x 106 2.25 x 1012
AAØZZ
FDIM 2003
May 15, 2003
16
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
- On each clock pulse the DDS performs
calculations
AAØZZ
FDIM 2003
May 15, 2003
17
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
- On each clock pulse the DDS performs
calculations
based on Frequency Tuning Word
AAØZZ
FDIM 2003
May 15, 2003
18
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
- On each clock pulse the DDS performs
calculations
based on Frequency Tuning Word
Current phase
AAØZZ
FDIM 2003
May 15, 2003
19
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
- On each clock pulse the DDS performs
calculations
based on Frequency Tuning Word
Current phase
- The DDS does look-up in sine table
AAØZZ
FDIM 2003
May 15, 2003
20
What Does A DDS Do?
DDS
D A C
F T W
01101011
Clock
- On each clock pulse the DDS performs
calculations
based on Frequency Tuning Word
Current phase
- The DDS does look-up in sine table
- The D-to-A Converter (DAC) sets output voltages
to desired levels
AAØZZ
FDIM 2003
May 15, 2003
21
Quadrature
AAØZZ
FDIM 2003
May 15, 2003
22
Block Diagram
LEDs
Clock
LP
Encoder
DDS
I out
Amp
Main
Filter
Encoder
PIC
PIC
LP
Q out
Amp
Filter
Push Buttons
Display
AAØZZ
FDIM 2003
May 15, 2003
23

• 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)

AAØZZ
FDIM 2003
May 15, 2003
24
Prototype Front
AAØZZ
FDIM 2003
May 15, 2003
25
Prototype Back
AAØZZ
FDIM 2003
May 15, 2003
26

• Software Description
• Encoder PIC microcontroller
• Main PIC Microcontroller
• Display (LCD)
• Pushbuttons and LEDs
• Dual VFO (Split Operation)
• Calibrate
• AD9854 Initialization

AAØZZ
FDIM 2003
May 15, 2003
27

• Results
• 2 Outputs Quadrature (900)
• 2-v p-p (10 dBm) I and Q
• 0 - 30 MHz
• Used in R2Pro (Don Huff, W6JL)
• - Its HOT!
• 40 dB Opposite Sideband Rejection
• -40 dB sounds astonishingly good
• Spurs?
• - Low (need more measurements)
• Phase Noise?

AAØZZ
FDIM 2003
May 15, 2003
28
Prototype Operational
AAØZZ
FDIM 2003
May 15, 2003
29
Prototype LCD
AAØZZ
FDIM 2003
May 15, 2003
30
HF-VFO with an R2Pro Receiver
(Rick Campbell, KK7B)
VFO
Antenna
Q
I
Analog
Audio
RF
Audio
Downconverter
Signal
Speaker
Filters
Amp
Amp
Processor
RF in
AAØZZ
FDIM 2003
May 15, 2003
31
Early Prototype Running R2Pro
Don Huff, W6JL
AAØZZ
FDIM 2003
May 15, 2003
32

• Extensions
• Add a Phase Lock Loop (PLL)
• Upgrade the 125 MHz reference clock
• Try different filter(s), amplifiers
• Add a CW sidetone
• Add Transmit/Receive keying delay logic for dual
  VFO operation
• Change the 5-V Regulator
• Add circuitry to change USB/LSB
• Experiment with spread spectrum

AAØZZ
FDIM 2003
May 15, 2003
33

• Conclusion
• Stable, usable VFO - as is
• Ready for your extensions
• Learning tool
• PIC microcontrollers
• DDS

AAØZZ
FDIM 2003
May 15, 2003
34
Questions?
AAØZZ
FDIM 2003
May 15, 2003