a 30 ghz real-time digitizing oscilloscope february 12, 2009
DESCRIPTION
A 30 GHz Real-Time Digitizing Oscilloscope February 12, 2009. Why Would You Need 30 GHz? Bandwidth requirements related to signal speed. 5 th harmonic. Power spectral density (dB). This plot shows Power Spectral Density (PSD) as a function of bit rate. - PowerPoint PPT PresentationTRANSCRIPT
A 30 GHz Real-Time Digitizing OscilloscopeFebruary 12, 2009
Why Would You Need 30 GHz?Bandwidth requirements related to signal speed
Normalized frequency in units of bit rateNormalized frequency in units of bit rate
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55thth harmonic harmonic
This plot shows Power Spectral Density (PSD) as a function of bit rate.
The plot is bounded by rise times that represent 0% (red line) or 100% (blue line) of a Unit Interval (UI)
Typically, serial data rise times are ~30% of a UI. There is significant PSD beyond the 5th harmonic frequency
Using an oscilloscope with bandwidth of 3x the bit rate or higher will show more frequency content
Bandwidth limiting of a 3 Gbps signal demonstrates need for more bandwidth
9 GHz bandwidth limited (3x bit rate)
7.5 GHz bandwidth limited (2.5x bit rate)
Serial data standards ≥2.5 Gb/sMinimum bandwidth requirements
SpecificationBit Rate Bandwidth (2.5x bit
rate)Bandwidth (3x bit
rate)
PCIE 2.0 2.5 Gbps 6.25 GHz 7.5
DisplayPort 1.1 2.7 Gbps 6.75 GHz 8.1 GHz
SATA 3 Gbps 7.5 GHz 9 GHz
SAS 3 Gbps 7.5 GHz 9 GHz
HDMI 1.3 a/b/c 3.4 Gbps 8.5 GHz 10.2 GHz
SuperSpeed USB 4.8 Gbps 5.76 GHz 14.4 GHz
SAS 6 Gbps 15 GHz 18 GHz
SATA 6 Gbps 15 GHz 18 GHz
Fibrechannel 8.5G 8.25 Gbps 20.625 GHz 24.75 GHz
PCIE 3.0 8 Gbps 20 GHz 24
10GBASEKR(802.3ap-2007
Backplane Ethernet)
10.3125 Gbps 25.78125 GHz 30.9735
Serial data transfer rate increases drive“Moore’s Law of Oscilloscope Bandwidth”
2000 Gigabit ethernet 1.25 Gbps
2001 SAS I 1.5 Gbps
2002 SATA I 1.5 Gbps
2003 PCI Express I 2.5 Gbps
2004 SAS I 3 Gbps
2005 XAUI 3.125 Gbps
2006 PCI Express II 5 Gbps
2007 SAS II 6 Gbps
2008 PCI Express III 8 Gbps
2009 10GBase-KR 10.3125 Gbps Dat
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As serial data transfer rates increase, the unit interval decreases and the rise time decreases, driving the need for more oscilloscope bandwidth
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2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
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ed (
GH
z)“Moore’s Law of Oscilloscope Bandwidth”Driven by Increasing data transfer rates and decreasing rise times
1st generation (6-8 GHz)
2nd generation (13 - 16 GHz)
“Moore’s law for bandwidth
Oscilloscope bandwidth
Problem – Serial data transfer rates and rise times of serial data signals require doubling of oscilloscope bandwidth every three years
Reality – Oscilloscopes must stay ahead of this curve while using the devices driving the curve
Methods for increasing oscilloscope bandwidth
DSP bandwidth boosting (stretching) Apply a digital filter to the acquired waveform that has a response which
peaks near the cutoff frequency of the input amplifier Peak in the filter response pushes the 3dB point up in frequency Can increase high frequency noise Sampling rate must be > 2X the boosted frequency Limited boost range based on the transition band of the input amplifier
Bandwidth interleaving Utilize RF hardware to digitize the signal in different frequency bands Use DSP filters to combine the separately digitized bands into one
waveform sampled at 2x the rate Front end amplifiers are always operating comfortably in rated frequency
range Reduces channel count but doubles the bandwidth No additional increase in high frequency noise Uses standard RF components (mixers, filters, amplifiers)
DSP bandwidth boostingNot the preferred method for increasing bandwidth
Amplifier responseDSP filter response
Boosted response
f fboosted
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Note: DSP “boost” or “stretch” should not be confused with other uses of DSP in oscilloscopes, such as to make minor response changes to match the response of channels and gain ranges or adjust phase delay. In the latter cases, DSP will provide signal fidelity improvements, not reductions.
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DSP bandwidth boosting is not a viable solution for meeting market demands
1st generation (6-8 GHz)
2nd generation (13 - 16 GHz)
“Moore’s law for bandwidth
Oscilloscope bandwidth
Tektronix attempted to keep up with “Moore’s Law of Oscilloscope Bandwidth” using a DSP boost (see yellow dotted line)
Unfortunately, the impact was limited, and oscilloscope bandwidth was again insufficient to meet market demand
Digitizer InterleavingAn accepted method to increase SR and memory
Bandwidth set by front-end amplifier
Lower speed digitizers and memory interleaved Improves sampling rate of A/D
Multiplies A/D converter sampling rate
Front-end amplifier
ADC’s
memory
Bandwidth InterleavingAn innovative method to stay ahead of the BW curve
Separate signal into frequency bands
Down-convert high band to low frequency
Digitize down-converted and low-band simultaneously
Use DSP to compensate delay, phase and amplitude and combine bands
40 G sa/s ADC’s
memory
16 – 30 GHz
1 – 15 GHz
0 – 16 GHz
DSP channel combiner
31.25 GHz LO
30 GHz @ 80 G sa/s
Bandwidth Interleaving – Animation
DBI Animation - Click Here
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2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
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ed (
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z)DBI allows oscilloscopes to keep up with “Moore’s Law of Oscilloscope Bandwidth”
1st generation (6-8 GHz)
2nd generation (15 - 16 GHz)
DBI
LeCroy’s DBI enables oscilloscopes to remain ahead of the bandwidth curve using current generation chip technology (solid yellow line)
LeCroy oscilloscope design allows for easy upgrade from 4 to 30 GHz bandwidth
WaveMaster 4 to 16 GHz acquisition board hardware
WaveMaster 20 to 30 GHz acquisition board hardware just adds DBI modules and 2.92mm
front panel connectors
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LeCroy WaveExpert sampling oscilloscope Measurement of “golden” step response
Input Step measured with WaveExpert Sampling Scope with 70 GHz sampler Usually subtract the input risetime from the measured risetime to get the
“scope only” risetime 22 Risetime InputRisetime MeasuredRisetimeOnly Scope
Step response measured on 30 GHz WaveMaster 830 Zi (DBI) oscilloscope
Shape of step and rise time value closely correlate with sampling scope
Step response measured on 30 GHz WaveMaster 830 Zi (DBI) oscilloscope
Oscilloscope bandwidth (top plot) shows response out to 30 GHz.
Conclusion
Bandwidth requirements are being driven by increasing transfer rates (and decreasing rise times) Oscilloscope hardware performance (amplifiers and A/D converters) is
set by the current technology Next generation hardware must be measured by current generation
technology
Oscilloscope bandwidth is being driven by a “moore’s law” which requires a doubling every 3 years
Bandwidth stretching using DSP cannot keep up with the bandwidth need and has limited performance
LeCroy’s Digital Bandwidth Interleaving (DBI) enables the doubling of current technology enabling measurements on next generation hardware
LeCroy’s DBI is the best way to achieve high bandwidth with appropriate signal fidelity