Transcript HF-VFO using an AD9854
HF-VFO using an AD9854 Direct Digital Synthesizer
Craig Johnson, AAØZZ FDIM 2003 May 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
AAØZZ FDIM 2003 May 15, 2003
Block Diagram
LEDs Encoder Encoder PIC Main PIC Clock DDS LP Filter LP Filter Amp I out Amp Q out Push Buttons Display
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word 2 48 AD9854 FTW = Desired Freq X ----------------- Frequency (Hz) AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word 2 48 AD9854 FTW = Desired Freq X ----------------- Frequency (Hz) 2 32 AD9850 FTW = Desired Freq X ----------------- Frequency (Hz) AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34 ~34 Million
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34 34.359738 x 10
6 AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34 34.359738 x 10
6 AD9854
:
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34 34.359738 x 10
6 AD9854
: ~2.25 x 10
6 AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
Frequency Tuning Word Examples (125 MHz Clock) 1 Hz 1 MHz AD9850
: 34 34.359738 x 10
6 AD9854
: ~2.25 x 10
6
~2.25 x 10
12 AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
- On each clock pulse the DDS performs calculations AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
- On each clock pulse the DDS performs calculations
based on: Frequency Tuning Word
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
Clock
- On each clock pulse the DDS performs calculations
based on: Frequency Tuning Word Current phase
AAØZZ FDIM 2003 May 15, 2003
What Does A DDS Do?
01101011
F T W
DDS
D A C
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
What Does A DDS Do?
01101011
F T W
DDS
D A C
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
Quadrature AAØZZ FDIM 2003 May 15, 2003
Block Diagram
LEDs Encoder Encoder PIC Main PIC Clock DDS LP Filter LP Filter Amp I out Amp Q out Push Buttons Display
AAØZZ FDIM 2003 May 15, 2003
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
Prototype – Front AAØZZ FDIM 2003 May 15, 2003
Prototype – Back AAØZZ FDIM 2003 May 15, 2003
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
• • • • • • •
Results
2 Outputs – Quadrature (90 0 ) 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?
AAØZZ FDIM 2003 May 15, 2003
Prototype – Operational AAØZZ FDIM 2003 May 15, 2003
Prototype – LCD AAØZZ FDIM 2003 May 15, 2003
HF-VFO with an R2Pro Receiver (Rick Campbell, KK7B)
Antenna RF in RF Amp VFO
I Q
Downconverter Analog Signal Processor Audio Filters Audio Amp Speaker
AAØZZ FDIM 2003 May 15, 2003
Early Prototype Running R2Pro Don Huff, W6JL AAØZZ FDIM 2003 May 15, 2003
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
AAØZZ FDIM 2003 May 15, 2003
Conclusion
• Stable, usable VFO - as is • Ready for your extensions • Learning tool PIC microcontrollers DDS
AAØZZ FDIM 2003 May 15, 2003
Questions?
AAØZZ FDIM 2003 May 15, 2003