Vertical Scaling Can Limit Resolution
8 bit ADC • 28 = 256 Q levels • Vertical setting = 1 V/div • 8 divisions • Full scale = 8V Each waveform is only using 7 of the 8 ADC bits. Resulting Resolution • 31 mV (8V / 256 levels)
5.
6. 7.
Use high-resolution mode to reduce noise
Bandwidth limit to reduce noise Average when signals are repetitive
8.
Use probes that have offset and required sensitivity
Need and Challenges
1. Start with a scope that has low noise.
– How do you characterize noise? – What different does noise make on precision signal viewing? – How do noise and ENOB compare? 2. Scale waveforms for maximum ADC resolution
ENOB between 8 and 9 bits (SNR between 50dB and 56dB) is typical for a 12-bit high-resolution digital oscilloscope
Unique ENOB value for each • Scope channel • V/div setting • Source frequency
3 Easy Steps 10 minutes total
1. Disconnect all inputs 2. Measure at each V/div setting 3. Measure Vrms AC on each channel
提示1：安捷伦9000H 250MHz~2GHz示波器同类产品中本底噪声最低 提示2：安捷伦90000X/Q 13GHz~63GHz磷化铟示波器同类产品中本底噪声最低 提示3: 安捷伦N2820A/21A探头量测精度业界最高，50uV 或 50uA
Oscilloscope Techniques for Precisely Measuring Small Signals
Teng Huang
Marketing Development Manager Agilent Technologies Greater China Oscilloscope Products Division Sep 5, 2013
Resulting Resolution • 16.5 mV (4V / 256 levels)
Associated Precision Signal Viewing Differences
提示1：安捷伦9000H 250MHz~2GHz示波器同类产品中本底噪声最低 提示2：安捷伦90000X/Q 13GHz~63GHz磷化铟示波器同类产品中本底噪声最低 提示3: 安捷伦N2820A/21A探头量测精度业界最高，50uV 或 50uA
提示2：安捷伦90000X/Q 13GHz~63GHz磷化铟示波器同类产品中ENOB最高
Need and Challenges
1. 2. Start with a scope that has low noise. Scale waveforms for maximum ADC resolution – Impact of scaling on precision signal viewing – Value of correct waveform positioning and multiple grids 3. Exploit the scope’s (off screen) dynamic range spec
Need and Challenges
Applications where needed
Need and Challenges
Challenges
Noise Impact on Precision Signal Viewing
Examples
Signal (DUT) Thick waveforms
Front-end Noise
Store each ADC output
Jagged waveforms
Scope display
Need and Challenges
1. 2. 3. 4. Start with a scope that has low noise. Scale waveforms for maximum ADC resolution Exploit the scope’s (off screen) dynamic range spec Use functions and duplicate waveforms to vertically zoom.
An ideal 8-bit ADC has an ENOB of 8 and a SNR of 50dB. Each additional effective bit improves the SNR by 6.02dB ENOB • varies with frequency, hence generally specified for a particular frequency. • good figure of merit when comparing oscilloscope technologies. • Result includes all noise and error sources in the oscilloscope including ADC quantization noise, ADC differential nonlinearity, ADC integral nonlinearity, thermal noise, shot noise, and input amplifier distortion. Expect an ENOB specification much lower than the number-of-bits specification due to these noise and error sources.
Compare of 2 Oscilloscopes with Equivalent Bandwidth
提示1：安捷伦9000H 250MHz~2GHz示波器同类产品中本底噪声最低 提示2：安捷伦90000X/Q 13GHz~63GHz磷化铟示波器同类产品中本底噪声最低 提示3: 安捷伦N2820A/21A探头量测精度业界最高，50uV 或 50uA
6.
7. 8.
Bandwidth limit to reduce noise
Average when signals are repetitive Use probes that have offset and required sensitivity
Characterizing Your Scope’s Noise
An Alternate Approach with Live Signal
1 Step 30 second noise approximation
With a low-noise signal 1. Turn on infinite persistence and measure the noise envelope Magnify function enables vertical zooming Caution: Is the noise from the scope or the DUT?
Need and Challenges
1. 2. 3. 4. Start with a scope that has low noise. Scale waveforms for maximum ADC resolution Exploit the scope’s (off screen) dynamic range spec Use functions and multiple windows to vertically zoom.
3.
Exploit the scope’s (off screen) dynamic range spec
4. 5.
Use functions and duplicate waveforms to vertically zoom. Use high-resolution mode to reduce noHale Waihona Puke se5.6. 7.
Use high-resolution mode to reduce noise
Bandwidth limit to reduce noise Average when signals are repetitive
8.
Use probes that have offset and required sensitivity
提示1：安捷伦9000H 250MHz~2GHz示波器同类产品中本底噪声最低 提示2：安捷伦90000X/Q 13GHz~63GHz磷化铟示波器同类产品中本底噪声最低 提示3: 安捷伦N2820A/21A探头量测精度业界最高，50uV 或 50uA
Resulting Noise Plot Characterization
4V
8V 4V
提示1：安捷伦9000H 250MHz~2GHz示波器是12比特的示波器 提示2：安捷伦9000A 和其它示波器是8比特的示波器