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Welcome! NEW LINK: https://training.ti.com/aerospace-defense-2020-webinar-series
Aerospace and Defense Webinar Series
• Every Tuesday at 2:30pm EST.
• Webinar WILL BE RECORDED and posted in LINK above
• Please send questions to TI contact who invited you to this session or use the chat feature in Webex
• Reminder: Multiple companies are on the line, please refrain from sharing anything proprietary.
• Please MUTE YOUR AUDIO
1
Texas Instruments
RF Sampling Converters Basics
2
Outline
• Dynamic Performance
– Noise contributions (thermal, jitter, quantization)
– Jitter breakdown (clock, aperture)
– Thermal noise impact to clock (slew rate)
• Frequency Planning
– DAC planning – keep wide swath of clear spectrum
– ADC planning – no interference in band
• Advanced System Features
– High BW (continuous or aggregate)
– Multi-band
• Dual DUC/DDC
• Multi-NCO (frequency agile, hopping, band monitoring)
– High Frequency
• Multi-Nyquist/high input BW - ADC
• Mixed mode, Multi-Nyquist DAC
• RF Sampling Roadmap Trends
3
Setting the Stage
• RF Sampling ADC Architecture
– Folding Interpolation
• High sampling rates 10 GSPS … pushing towards 50 GSPS
• 12-bit performance with reasonable power consumption
– Pipeline
• Core sample rates at 3 GSPS … pushing towards 10 GSPS
• 14-bit performance with good power consumption
• RF Sampling DACs
– 14-bit operating up to 12 GSPS – support 6 GHz RF in 1st Nyquist zone
– Multi-mode operation to operate in 2nd Nyquist zone (or higher) up to 12 GHz
4
Anatomy of the RF Sampling Converter
5
SNR Contribution Breakdown
• Total SNR can be calculated by the sum of the individual sources:
– SNRQuant: SNR due to quantization noise (typically out of the picture)
𝑆𝑁𝑅𝑄𝑢𝑎𝑛𝑡 = 6.02𝑁 + 1.76 𝑑𝐵
– SNRTherm: SNR due to thermal noise
– SNRJitter: SNR due to clock and aperture jitter
𝑆𝑁𝑅𝑇𝑜𝑡𝑎𝑙 = −10log 10−𝑆𝑁𝑅𝑄𝑢𝑎𝑛𝑡
10 + 10−𝑆𝑁𝑅𝐽𝑖𝑡𝑡𝑒𝑟
10 + 10−𝑆𝑁𝑅𝑇ℎ𝑒𝑟𝑚
10
6
Thermal
Clock Jitter
Aperture Jitter
Quantization
Jitter Impact with respect to Frequency
• SNR is independent of sampling rate
• SNR is dependent on input frequency
– For a given amount of jitter, SNR degrades as input
frequency increases
• Higher sampling rates indirectly lead to more
stringent jitter requirements
– High sampling rate device are not “more sensitive”;
rather, high sampling rates allow higher input
frequencies
Clk
IF1
IF2
t=Jitter
)2log(20 jinj fSNR
Jitter Contributions
• The total clock jitter for a data converter is sum of:
– Clock jitter: jitter contribution from the external clock source; measured with a phase
noise analyzer
– Aperture jitter (a.k.a. aperture uncertainty): jitter contribution from the internal clock
path of the data converter; value taken from datasheet
• Total clock jitter is the rms sum of individual contributors
𝜏𝐽𝑖𝑡𝑡𝑒𝑟 = 𝜏𝐶𝑙𝑘2 + 𝜏𝐴𝑝𝑒𝑟𝑡𝑢𝑟𝑒
2
• Critical to provide lowest phase noise, lowest jitter clock for best SNR
9
Impact of Wideband Clock Noise
10
Input Signal Clock Signal
Clock bandwidth typically
limited to 2Fs
• Input signal and clock signal
• Clock (signal+noise) effectively “mix
down” to input signal
• All noise aliases down to 1st Nyquist
zone
• Low clock noise floor or clock band-pass
filter is critical
n
t
Slew Rate and Jitter Performance
• Slower slew rate is more susceptible to zero crossing variations due to noise
• BPF filters broadband noise but also removes harmonics
– Square-wave-like clocks become sinusoid clocks
– Sinusoid signals have lower slew rate
• Increase signal to large amplitude to minimize slew rate impact
11
n
t1
t2
Reality of RF Sampling Transmitter
12
Freq Fs/2 band
HD2 HD3 Clk Mix
Fs/2 - RF …
Filter 2nd Nyquist
Image RF
• Ideal Transmitter: Fundamental signal at the frequency of interest
• Real World Impairments:
– HD2, HD3 (aliased) Component
– Clock Mixing, Fs/2 Spurious
– Image Frequency in 2nd (and higher) Nyquist zone
• Analog filter added to minimize/eliminate spurious outputs
Strategy for Spectral Mask with RF DAC
• Meeting in-band spectral mask
– No filtering is possible; inherent performance must meet mask
– Frequency plan to move known spurious product outside of band
• Meeting out-of-band spectral mask
– Optimize sampling rate to move spurious far away from desired band
– Incorporate filtering to suppress out-of-band spurious from being transmitted
– Farther the separation of spurious products, the easier to filter
– With proper planning, filtering eliminated or relaxed compared to other architectures 13
Freq
Fs/2 RF DAC …
Filter
TX Frequency Planning Example RF = 2140 MHz; BW = 60 MHz
• Fs = 6144 MHz
• In-band is clear but HD2 and HD4 are close
and hard to filter
• Increase sampling rate:
– Fs = 8024 MHz
• In band still clear but HD3, HD5, and Clock
mixing spur hard to filter
• Decrease sampling rate:
– Fs = 5683.2 MHz
• In-band clear and lots of spacing to other
spurious easy filtering
14
Reality of RF Sampling Receiver
• Real World Spectral Impairments
– Spurious signals (i.e. IM3, HD2, HD3 etc.) from in-band interferers generated in analog chain (i.e.
LNA, VGA)
– Out-of-band Interferers from Blockers/Jammers
– TX signal bleed-through to the RX path
– IM3 Mixing products between Jammers and TX bleed-thorough
• Real World Overdrive Impairments
– TX Bleed-through
– Blockers/Jammers
• Broadband Noise folding into 1st Nyquist Zone
Freq Fs/2 Band
RF ADC
15
Strategy for Maintaining Sensitivity w/ RX
• Duplexer Filter
– Suppresses TX Bleed-through into receiver
– Eliminates IM3 Spurious generation
• Channel Filter
– Suppress out-of-band spurious generated from in-band interferers
– Suppress Blocker signals
– Suppress harmonic/mixing spurs from blocker(s)
• Anti-aliasing filter to eliminate broadband noise
Freq Fs/2 band
RF ADC
Duplexer Filter
Channel Filter
16
RF Sampling ADC - Frequency Planning
• Spurs from out-of-band interferers or TX bleed-through – Proper filtering can minimize or eliminate these threats
• Spurs from in-band interferers – Can not filter these signal out
– Need to frequency plan around
• Higher sampling rate affords flexibility in frequency planning around troublesome harmonic and spurious products
• Frequency planning in High IF systems – Choose available sampling rate converter
– Optimize IF location for best results
• Frequency Planning in RF Sampling – Can not choose location of RF signal; this is fixed
– Optimize sampling rate to achieve best results
17
Frequency Planning Example
• Case 1: High IF Sampling
– Fs = 500 MHz
– IF = 375 MHz
– BW = 100 MHz
• Can not escape from aliased
HD2 and higher harmonics
• Case 2: RF Sampling
– Fs = 6144 MHz
– BW = 100 MHz
– RF = 1950 MHz
• Higher order harmonics do
not fall in band
18
High Bandwidth - Multi-band Operation
• Signal BW does not need to be contiguous
– i.e. Two smaller BW signal separated in frequency considered as one larger signal BW
• RF Sampling solution provides a mechanism to support multiple bands, each
with arbitrary signal bandwidth and with variable spacing
19
Band 1 Band 2
BW1 BW2
System BW
High Bandwidth / Flexibility - Tunable
• Allocated RF Frequency Band is pre-defined
– i.e. defined from standards requirement, regulatory requirements, or from system
specifications
• Within the allocated band, desired signal can be assigned to specific (narrow
band) channel
• RF Sampling Solution provide mechanism to easily place/capture desired signal
at any arbitrary channel.
20
Multiple NCO – Multi-Band
• Include multiple NCOs to tune separate channels to arbitrary RF frequency
location
– Supports non-contiguous multi-carrier operation
– Supports multi-band or multi-mode operation
• Keeps input data rates low; sufficient to meet bandwidth requirements of each
signal
• Supports very wide effective output bandwidth
21
NCO – Numerically Controlled Oscillator
• Includes 2 switchable NCOs
– NCOs programmed via SPI
– Switch accomplished via SPI or GPIO
• Why multiple NCOs?
– Switch to different bands quickly: calibration purposes, band flexibility, etc.
– Quick frequency hopping
• Resolution
– 32-bit Resolution = 𝑁 ∗𝐹𝑠
232
– Fixed 5 kHz raster with Reference = N*61.44 MHz
• All NCOs maintain phase 22
NCO Phase Cohesion
23
Phase
information
retained
Synchronization
maintained when
frequency shifting
Standard Zero-order Hold Sampling AKA Non-return to Zero (NRZ)
24
1st N
yquis
t
2n
d N
yquis
t
Reference: Digital-to-Analog Converter (DAC) Output Response presentation at ti.training.com
Mixed Mode DAC AKA Return-to-Complement (RTC)
25
1st N
yquis
t
2n
d N
yquis
t
Mixed Mode Option
• Mixed mode provides option to use 2nd Nyquist zone
• Operation up to 6 GHz output
– 1st Nyquist zone with 12 GHz clock
– 2nd Nyquist zone with 6 GHz clock
Saves power
• Operation above 6 GHz possible in mixed mode operation with 12 GHz clock
26
Inverse SINC filter
• Digital pre-emphasis filter corrects for the expected SINC response
– Zero-Order hold – 1st Nyquist operation
– Mixed Mode - 2nd Nyquist Operation
• Digitally back-off signal to account for iSINC gain to avoid saturation
Dis
cre
te A
DC
/DA
C
An
alo
g F
ron
t E
nd
s
RF Sampling Roadmap Trends
Released Sampling
1.6x BW increase
Multi-Channel Integration
DAC38RF80/83/90/93 • Dual, 14-bit 9-GSPS DAC • Internal PLL/VCO
ADC12J4000 • Single, 12-bit 4-GSPS ADC
AFE74xx • 4T4R • 9-GSPS DAC / 3-GSPS ADC • Integrated DSA / PLL/VCO
AFE7950/00 • 4T6R – 30M-12GHz • Integrated DSA / PLL/VCO • BW: 2.4 / 1.2 GHz TX / RX
ADC12DJ3200 • Dual, 12-bit 3.2-GSPS ADC • Single, 12-bit 6.4-GSPS ADC
ADC12QJ1600 • Quad, 12-bit 1.6-GSPS ADC
ADC12DJ5200 • Dual, 12-bit 5.2-GSPS ADC • Single, 12-bit 10.4-GSPS
2x Channel Integration
1.5x Power Reduction
4 Channel Integration 2x BW increase
Higher SNR
ADC32RF80/83 • Dual, 14-bit 3-GSPS ADC • 4-GHz input BW • NSD = -155 dBFS/Hz
2x Power Reduction
FB Channel Integration
2x SerDes Speed
2x Frequency Range
Development
AFE80xx • Coming 2021
DAC39RF10 • High Performance • Multi-Nyquist DAC
ADC32RF54 • High Performance • Multi-Nyquist ADC
Texas Instruments Check Out High Speed Signal Chain University for more information: https://training.ti.com/high-speed-signal-chain-university