ddc personality status

DDC Personality StatusOctober 2011 – Matt Luce

1

2

Overview

• Block Diagram• Version 1.0 Problems• Version 1.1

– PFB– Weaver

• Future Improvements– Version 1.2 and beyond

3

DDC Block Diagram

4

1.0 Typical Spectrum

550 600 650 700 750 800 850 900 950 1000

-25

-20

-15

-10

-5

0 X: 610Y: 0.5297

stitched bandpass from 64MHz BW channels

X: 670Y: -12.35

X: 866Y: -9.861

5

1.0 Problems w/PFB

• PFB is generating large spurious tones

• PFB sub-band edges are too soft– >32MHz dead-zones

between sub-bands to avoid aliasing

550 600 650 700 750 800 850 900 950 1000

-25

-20

-15

-10

-5

0 X: 738Y: 0.3902


X: 542Y: -9.384

X: 798Y: -17.73

X: 994.1Y: -4.289

6

1.0 Problems w/down-converters

• Weaver IR filter is not sharp enough and is creating aliases.

• Cleanup/weaver filters are creating too many ripples in the pass-band.

550 600 650 700 750 800 850 900 950 1000

-30

-25

-20

-15

-10

-5

0

X: 613Y: -21.38


X: 539Y: 1.538

7

1.0 Problems w/Decimation

• Limited BW support– 64MHz and 16MHz are the only completely functional– CIC output truncation is critical!

8

What is version 1.1?

• Architecture: 2 down-converters• Improved filter responses

– Poly-phase– Weaver image reject– CIC cleanup

• Improved down-converters– Supported Bandwidths: 64MHz, 32MHz, 16MHz…

62.5kHz• Mark5B

– Format select: 1 or 2 streams• Bug fixes!

9

Large Spurious Signals

1.0 (append) 1.1 (sign extend)

550 600 650 700 750 800 850 900 950 1000

-30

-25

-20

-15

-10

-5

0X: 660Y: 1.357


X: 781.3Y: -22.04

550 600 650 700 750 800 850 900 950 1000

-25

-20

-15

-10

-5

0 X: 738Y: 0.3902


X: 542Y: -9.384

X: 798Y: -17.73

X: 994.1Y: -4.289

10

Improved Poly-phase Filter Bank

1.0 (80) 1.1 (128)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-70

-60

-50

-40

-30

-20

-10

0

Normalized Frequency: 0.25Magnitude: -6.0206



Normalized Frequency ( rad/sample)

Mag

nitu

de (

dB)

Magnitude Response (dB)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-70

-60

-50

-40

-30

-20

-10

0





Mag

nitu

de (d

B)


11

Improved Weaver IR Filter

Old (20) New (128)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0





Mag

nitu

de (d

B)


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-70

-60

-50

-40

-30

-20

-10

0

Normalized Frequency: 0.4940186Magnitude: -3.032166 Normalized Frequency: 0.5

Magnitude: -6.0206



Mag

nitu

de (

dB)


12

SB-SB Aliasing (1.1)

636MHz 650MHz

13

Improved CIC Cleanup Filter

1.0 (40) 1.1 (128)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-70

-60

-50

-40

-30

-20

-10

0

Normalized Frequency: 0.4940186Magnitude: -3.032166 Normalized Frequency: 0.5

Magnitude: -6.0206



Mag

nitu

de (

dB)


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0





Mag

nitu

de (d

B)


DSP Slice Budget: 640 Available

• Channelization (2)– 128 per IF

• DC (2):– Mixers (DDS +

multipliers)• 6 per DC

– Image reject FIR• 68 per DC

– CIC & cleanup FIR:• 34 per DC

– 216 total• TOTAL: 472 (~70%)

freeused

15

Spectrum: 488 FFT Bench

660 680 700 720 740 760

-25

-20

-15

-10

-5

0X: 739Y: 2.168

stitched plot: 64MHz channels

16

Spectrum: Bench 0Baseline

17

Spectrum: VLBA Single station auto-correlationsTD023C

18

The Future

• 1.1.1 (Experimental version)– Hilbert SSB

• 1.2– Partial support for128MHz BW

• 512-640MHz• 896-1024MHz

– Tsys (w/ quantizer)• 1.3

– Full support for 128MHz BW– Pipeline delay correction

ddc personality status

Documents