ADCs for Software Radios - ITS

Solutions for Digital Radioa 3/4/99 - 1

ADCs for Software Radios

Presented by:

Tom Gratzek

Analog Devices Inc.

Greensboro, NC

336-605-4233/[email protected]


Commercial Application Drivers

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12

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16

18

20

22

24

1 0 0 E + 0 1 E + 3 1 0 E + 3 1 0 0 E + 3 1 E + 6 1 0 E + 6 1 0 0 E + 6 1 E + 9 1 0 E + 9

Sample Rate (S/s)

Nom

inal

Res

olut

ion

(bits

)

Audio

Physical Measurments

Wired Coms (XDSL)

UltraSound

Video Digitizerscam corders

Sat Rx/Drives

Cable Modems

HandheldEquipment

Instrumentation

Analyzers - Scopes

POTSWireless handsets Imaging

Base Stations


Fabrication Processes

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10

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18

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22

24

1 0 0 E + 0 1 E + 3 1 0 E + 3 1 0 0 E + 3 1 E + 6 1 0 E + 6 1 0 0 E + 6 1 E + 9 1 0 E + 9

Sample Rate (S/s)

Nom

inal

Res

olut

ion

(bits

)

ADC as block system chip

Stand-aloneCMOS ADCs

Si - Bipolar

Efficiency(mW/MHz)

220

25

10

3

2

1.5


ADC Technology Trends

• Applications drive technology development

• At volume, ADC function moves to SOC block

– disk drives, pro audio, ADSL, cable modems,NB radios, scanners, digital cameras

• Technology Development Trends (12 bit 20MSPS)Year P. Diss. Tech. Dyn. Perf. Cost Application

84 20 W Board 60 dB $4K Radar

88 5 W Hybrid 62 dB $1K Missiles

92 2 W bipolar 63 dB $200 Instruments

96 0.4W CMOS 65 dB $20 Medical98 0.2W core 65 dB $2 Image. ASIC


ADC: Not all created equal

• Critical specifications for radio applications

• Dynamic range - correlates with # of bits?

– SNR, Harmonic distortion, SFDR• may only roughly correlate with nominal # of bits

– Aperture jitter - limits at high input frequency

• Sample rate - must obey Nyquist criteria

– IF sampling performance

– must understand channel bandwidth vs. IF


What Kind of Software Radio?

• Software radio - adaptive bandwidth & modulation?

– Narrowband PCS• 25, 12.5, 6.25 KHz BW by same radio

• Must provide service for 1 month on single A Cell

• Tune at RF, Sigma Delta ADC, extremely low power

– Programmable base station (Macro)• Multiple channels in licensed band (15 MHz)

• Various types of signals in band (IS-136, CDMA, GSM)

• Tune and filter in digital domain

• ADC linearity often limits receiver performance


ADC Errors effect Receivers

• Static Errors– non linearity in encoder transfer function

– can create harmonics in frequency domain

• Dynamic Errors– sampling jitter - increases noise at high Ain

– T/H linearity - increase in noise & harmonics

• Noise– sampling, component, thermal


ADC error avoidance Techniques

• Oversampling -

– decreases noise in band of interest (improves SNR)

– facilitates digital filtering/ “processing gain”

• Dither -– smooths the encoder transfer function reducing

spurs (requires excellent T/H at high Ain)

• IF sampling -

– can move harmonics out of analysis bandwidth

– can filter amp harmonics with IF filters &reduce analog component count


1st Nyquist Zone Full Band ADC Per form a n c e

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0 5 10 15 20 25 30 35

Frequency (MHz)

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AD6640: -80 dBfs Spurs

Sampling rate = 65MSPS; dc to 32.5MHz; Ain = 15.5 MHz


1st Nyquist Zone Narrow Band ADC Performance

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12.5 13.5 14.5 15.5 16.5 17.5 18.5

Frequency (MHz)

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AD6640-1st Nyquist Performance

Sampling rate = 65MSPS; 12.5 to 18.5MHz; Ain = 15.5 MHz


3rd Nyquist Zone Full Band ADC Performance

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AD6640 3rd Nyquist Zone

Sampling rate = 65MSPS; 65 to 97.5 MHz; Ain = 80.5 MHz


200 MHz Performance

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193 198 203 208 213 218 223

Frequency (MHz)

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AD6640: 7th Nyquist Zone

Sampling rate = 65MSPS; 193 to 225MHz; Ain = 200 MHz


200 MHz Performance of the AD6640 (5 MHz Band)

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197.5 198 198.5 199 199.5 200 200.5 201 201.5 202 202.5

Frequency (MHz)

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Sampling rate = 65MSPS; 197.5 to 202.5 MHz; Ain = 200 MHz

7th Nyquist Zone - Zoom


Processing Gain & Oversampling

Standard Chan. BW Symbol Rate Samp. rate Proc.Gain*IF SamplingIS-136 30 KHz 48.6 Kbit/sec 9.72 MSPS 22 dB

GSM 200 KHz 270.83 Kbit/s 6.5 MSPS 12 dB

CDMA 1.23 MHz 1.228 Mbits/s 19.66 MSPS 9 dB

Wide bandIS-136 30 KHz 48.6 Kbit/sec 58.32 MSPS 29 dBGSM 200 KHz 270.83 Kbit/s 65 MSPS 22 dB

CDMA 1.23 MHz 1.228 Mbits/s 58.98 MSPS 14 dB3G 5MHz 4.096 Mbits/s 65.53 MSPS 9 dB

* Assumes 1 sample/symbol

Processing Gain = 10 log (Sample rate/2* channel BW)


Multi-Channel RX Challenges

RF/IF stagereceiver

DSPChannel

1

DSPChannel

2

DSPChannel

n

Digital Filter(channelizer)



ADCRadioBaseStation

PublicTelephoneNetwork

High SFDRADC

High DynamicRange Radio


AD6620 FunctionsNCO and Filter Stages

Real,Dual Real,

or ComplexInputs

OutputFormat

RAMCoefficient

Filter

CIC5Filter

CIC2Filter

ComplexNCO

cos -sin

I

Q

I

Q

I

Q

I

Q

Serial orParallelOuputs

Dual Channel Decimating ReceiverAccepts real or complex input words: provides tuning and decimation filtering65 MSPS Single channel inputs or 32.5 MSPS Dual Channel ModeNCO worst spur better than -105dBc; 0.02 Hz tuning resolutionCIC2 Fixed Coefficient Filter decimates 1 to 16; CIC5 Fixed Coefficient Filter decimates 1 to 32Programmable RAM based FIR filter with programmable decimates 1-32 1700 Million Operations per second at 250 micro-watts/MOP

AD6620


Design Filter Using AD6620software


Modular Evaluation Boards

AD6640 - 12 bit 65MSPS IF Sampling ADC

AD6620 Receive Signal Processor

AD6600 - Diversity Receiver ADC


RF/IF stagereceiver

DSPChannel

1

DSPChannel

2

DSPChannel

n




ADC

RadioBaseStation Public

TelephoneNetwork

Frequency

SignalStrength

Frequency

SignalStrength

Frequency

SignalStrength

Frequency

SignalStrength

Multi-carrier Receivers Overview


W ideband GSM receiver (AD6640+AD6620)

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12.5 13.5 14.5 15.5 16.5 17.5 18.5

F r e q u e n c y ( M Hz)

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AD6640 + AD6620: GSM

Sampling rate = 65MSPS; IF = 12.5 MHz to 18.5 MHz (noise floor increased due to lower decimation rate)


W ideband GSM receiver (AD6640+AD6620)

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Fre

q

12.7

1111

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12.9

2111

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13.1

3111

1

13.3

4111

1

13.5

5111

1

13.7

6111

1

13.9

7111

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14.1

8111

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14.3

9111

1

14.6

0111

1

14.8

1111

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15.0

2111

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15.2

3111

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15.4

4111

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15.6

5111

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15.8

6111

1

16.0

7111

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8111

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16.4

9111

1

16.7

0111

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16.9

1111

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17.1

2111

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17.3

3111

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17.5

4111

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17.7

5111

1

17.9

6111

1

18.1

7111

1

18.3

8111

1

Frequency (MHz)

Am

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Hz)

GSM:Pico Cell - Y/ Macro - N

Yellow - Pico Cell Mask; Purple - Macro Cell Mask;


I F Sampl ing W ideband GSM receiver (AD6640+AD6620)

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1111

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12.9

2111

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13.1

3111

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4111

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5111

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6111

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7111

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14.1

8111

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14.3

9111

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0111

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14.8

1111

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15.0

2111

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15.2

3111

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15.4

4111

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15.6

5111

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15.8

6111

1

16.0

7111

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16.2

8111

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16.4

9111

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0111

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1111

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17.1

2111

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17.3

3111

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4111

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5111

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17.9

6111

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18.1

7111

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18.3

8111

1

Frequency (MHz)

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GSM Receiver: IF Sampling

Yellow - Pico Cell Mask; Purple - Macro Cell Mask;

Sampling Rate: 65MSPS; Ain 77.5 to 83.5 MHz


W ideband IS-136 receiver (AD6640+AD6620)

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12.5 13.5 14.5 15.5 16.5 17.5 18.5

Frequency (MHz )

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AD6640 + AD6620: IS-136

Sampling rate = 65MSPS; IF = 12.5 MHz to 18.5 MHz (noise floor reduced due to narrow IS-136 filter)


W ideband

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Fre

q

12.7

0111

1

12.9

0111

1

13.1

0111

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13.3

0111

1

13.5

0111

1

13.7

0111

1

13.9

0111

1

14.1

0111

1

14.3

0111

1

14.5

0111

1

14.7

0111

1

14.9

0111

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15.1

0111

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15.3

0111

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15.5

0111

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15.7

0111

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15.9

0111

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16.1

0111

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16.3

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0111

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17.1

0111

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17.3

0111

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0111

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17.7

0111

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17.9

0111

1

18.1

0111

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18.3

0111

1

Frequency (MHz)

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Meets IS-136 Specification

Sampling rate = 65MSPS; IF = 12.5 MHz to 18.5 MHz (noise floor reduced due to narrow IS-136 filter)


Narrowband Chipsetcomparison (IF to digitizer(s))

AD6600 DSPAD6620

AD6630200 MHz

IF

AD6630

200 MHzIF

ADC

DACRSSI

LO

ADC

LO

$ Hi selectivityfilter

10.7 MHzfilter Baseband I&Q

Demod, filter, & digitize

DSP

Traditional: Two channels required for diversity total cost = $200+

total cost <$100


GSM, IF sampling Ref. Design


“IF” Gain-Ranging Technology

DiversityRF stagereceiver

IF stagereceiver

DSPChannel

1ADC

Digital Decimate

Filter

FLT+ FLT-

ATTENVIN A-

+

ATTENVIN B-

+

3RSSI

GND VCC

DIGITALOUTPUTS

AB_OUT

T/H11

TIMING

ENC A_SEL B_SEL

3

GAIN

3

RSSICONTROL

2X CLKOUT

PEAKDETECTOR

ENC

EXTERNAL LCNOISE FILTER

56011-BITADC70-250 MHz IF

MainChannel

DiversityChannel

20 MSPSDigital DataWords Out

Signal range = 30dB AGC + 60dB ADC = 90dB


Sampling 170 MHz IF


GSM IF Strip 167-173 MHz (SAWS+AD6630+AD6600+AD6620)

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IF sampling chipset:meets GSM requirements

Sampling rate = 6. 5MSPS; IF = 167 MHz to 173 MHz


Conclusions

• ADC technology improving dramatically in many ways• ADC manufacturers need volume applications to drive

R/D investment• System understanding drives ADC innovations• Multi-mode, Multi Channel Rx chipsets available

– performance limited by ADC• IF Sampling Chipset (AD6600+6620+6630)

– available and meets GSM requirements

– requires some analog filtering

– High IF sampling decreases “RF” costs


More Information

• AD6640, AD6620, AD6630 and AD6600 chips,app notes and evaluation boards available fromAnalog Devices

• search at www.analog.com

ADCs for Software Radios - ITS

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