AD9911DDS

         

AD9911DDS Release status: experimental [box doku]
Description	Direct Digital Synthesizer
Author(s)	siro
Last Version	0.1
Platform	*
License	GPL

AD9911DDS

This project describes the AD9911 Direct Digital Synthesizer. It is capable of generating a sine-wave between 250Mhz and >1Hz. The created evaluation unit is descripted here.

The Hardware

• CLK_MODE_SEL = 1.8V
• Rset = 1k91
• crystal 25Mhz
• DVDD 1.8V
• AVDD 1.8V
• DVIO 3.3V
• SDIO_0 MOSI
• SDIO_2 MISO
• PLL 20x, 500MSPS DAC
• maximum frequency possible 250Mhz
• maximum frequency recommended 150Mhz
• low pass required
• active current 120mA
• output AC coupled

channels

There are four channels:

• channel 0: aux channel
• channel 1: primary channel
• channel 2: aux channel
• channel 3: aux channel

channel 1 is connected to the DAC. all aux channels are capable of modulating channel 1.

modes of operation

• single tone (frequency,amplitude,phase adjustable)
• 2 tone test mode (amplitude modulated single tone)
• 2/4/8/16 FSK/ASK/PSK
• frequency/amplitude/phase ramp up
• frequency/amplitude/phase ramp down
• frequency/amplitude/phase sweep

SPI interface

default
2-wire SPI mode, SDIO_0 is bidirectional !

• SPI write
  • CPOL=0
  • CPHA=0
• SPI read
  • CPOL=1
  • CPHA=1

3-wire SPI mode

• configure 3-wire SPI mode using reg 0
• set msb mode (default) using reg 0
• SDIO_0 is MOSI
• SDIO_2 is MISO

MSB/LSB mode

• MSB
  • the Most Significant Bit is transfered first
  • the Most Significant Byte is transfered first
• LSB
  • the Least Significant Bit is transfered first
  • the Least Significant Byte is transfered first

register select

• register 0, 1, 2 are independent
• channel register 0x03 - 0x18 are written to using the enable bits in register 0
• you can write to multiple channels at once !

*TODO upload files*

The Software

I've created a simple programm that runs on teensy 2.0 (ATMEGA32U4). It should run on any ATmega, just change the I/O ports.
Timings are not critical, as the ATmega is much slower than the maximum I/O updaterate of the AD9911.
Software flow:

• write register 0 (channel select bits)
• write register 1 and 2 (digital power down, pll multiplier)
• write to selected channel registers 0x03 - 0x18
• toogle I/O-Update pin

*TODO upload files*

Changes applied to Hardware

• pull PWR_DWN_CTL low
• pull SDIO_3 low
• terminate IDAC with 50 Ohms agains AVCC
• terminate !IDAC with 50 Ohms agains AVCC
• include a 5th order low pass filter
• include a transformer
• series resistance for SPI interface
• third order 200Mhz low pass

Results

AD9911 Devboard PCB soldered