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

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Block Diagram

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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

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DDS01101011

Clock

DAC

FTW

What Does A DDS Do?

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DDS01101011

Clock

DAC

FTW

Frequency Tuning Word

What Does A DDS Do?

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DDS01101011

Clock

DAC

FTW

Frequency Tuning Word

AD9854 FTW = Desired Freq X ------------------ 248

Frequency (Hz)

What Does A DDS Do?

FDIM 2003May 15, 2003

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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?

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DDS01101011

Clock

DAC

FTW

Frequency Tuning Word Examples (125 MHz Clock)

What Does A DDS Do?

FDIM 2003May 15, 2003

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DDS01101011

Clock

DAC

FTW

Frequency Tuning Word Examples (125 MHz Clock)

1 Hz 1 MHz

What Does A DDS Do?

FDIM 2003May 15, 2003

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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

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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

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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

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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

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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

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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

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DDS01101011

Clock

DAC

FTW

- On each clock pulse the DDS performs calculations

What Does A DDS Do?

FDIM 2003May 15, 2003

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DDS01101011

Clock

DAC

FTW

based on: Frequency Tuning Word

- On each clock pulse the DDS performs calculations

What Does A DDS Do?

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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

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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

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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

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FDIM 2003May 15, 2003

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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

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Prototype – Front

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Prototype – Back

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Software Description

• Encoder PIC microcontroller

• Main PIC Microcontroller

• Display (LCD)

• Pushbuttons and LEDs

• Dual VFO (Split Operation)

• Calibrate

• AD9854 Initialization

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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

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Prototype – Operational

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Prototype – LCD

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HF-VFO with an R2Pro Receiver

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AudioFilters

AnalogSignal

ProcessorDownconverter

VFO

I Q

RFAmp

AudioAmp

Antenna

RF inSpeaker

(Rick Campbell, KK7B)

Early Prototype Running R2ProDon Huff, W6JL

FDIM 2003May 15, 2003

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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

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Conclusion

• Stable, usable VFO - as is

• Ready for your extensions

• Learning tool

PIC microcontrollers

DDS

FDIM 2003May 15, 2003

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Questions?

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