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Direct Digital Synthesizer
HF-VFO using an AD9854 Direct Digital Synthesizer Craig Johnson, AAØZZ FDIM 2003 May 15, 2003
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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
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Block Diagram DDS LEDs Clock Encoder LP Amp Main I out Encoder Filter
PIC PIC LP Amp Q out Filter Push Buttons Display AAØZZ FDIM 2003 May 15, 2003
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What Does A DDS Do? DDS 01101011 Clock F D T A W C AAØZZ FDIM 2003
May 15, 2003
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What Does A DDS Do? DDS 01101011 Clock Frequency Tuning Word F D T A W
AAØZZ FDIM 2003 May 15, 2003
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AD9854 FTW = Desired Freq X ------------------
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word 248 AD9854 FTW = Desired Freq X Frequency (Hz) AAØZZ FDIM 2003 May 15, 2003
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What Does A DDS Do? DDS 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
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: ~34 Million AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: x 106 AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: x 106 AD9854: AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: x 106 AD9854: ~2.25 x 106 AAØZZ FDIM 2003 May 15, 2003
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Frequency Tuning Word Examples (125 MHz Clock)
What Does A DDS Do? DDS F T W D A C Clock Frequency Tuning Word Examples (125 MHz Clock) 1 Hz MHz AD9850: x 106 AD9854: ~2.25 x ~2.25 x 1012 AAØZZ FDIM 2003 May 15, 2003
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- On each clock pulse the DDS performs calculations
What Does A DDS Do? DDS F T W D A C Clock - On each clock pulse the DDS performs calculations AAØZZ FDIM 2003 May 15, 2003
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- On each clock pulse the DDS performs calculations
What Does A DDS Do? DDS F T W D A C Clock - On each clock pulse the DDS performs calculations based on: Frequency Tuning Word AAØZZ FDIM 2003 May 15, 2003
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- On each clock pulse the DDS performs calculations
What Does A DDS Do? DDS F T W 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
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What Does A DDS Do? DDS 01101011 Clock
F T W 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
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What Does A DDS Do? DDS 01101011 Clock
F T W 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
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Quadrature AAØZZ FDIM 2003 May 15, 2003
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Block Diagram DDS LEDs Clock Encoder LP Amp Main I out Encoder Filter
PIC PIC LP Amp Q out Filter Push Buttons Display AAØZZ FDIM 2003 May 15, 2003
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Hardware Description 2 PIC Microcontrollers AD9854 DDS 5-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
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Prototype – Front AAØZZ FDIM 2003 May 15, 2003
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Prototype – Back AAØZZ FDIM 2003 May 15, 2003
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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
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Results 2 Outputs – Quadrature (900) 2-v p-p (10 dBm) I and Q
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
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Prototype – Operational
AAØZZ FDIM 2003 May 15, 2003
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Prototype – LCD AAØZZ FDIM 2003 May 15, 2003
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HF-VFO with an R2Pro Receiver
(Rick Campbell, KK7B) VFO Antenna I Q Analog RF Audio Audio Downconverter Signal Speaker Amp Filters Amp RF in Processor AAØZZ FDIM 2003 May 15, 2003
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Early Prototype Running R2Pro
Don Huff, W6JL AAØZZ FDIM 2003 May 15, 2003
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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
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Conclusion Stable, usable VFO - as is Ready for your extensions
Learning tool PIC microcontrollers DDS AAØZZ FDIM 2003 May 15, 2003
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Questions? AAØZZ FDIM 2003 May 15, 2003
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