1 dr. un-ki yang particle physics group [email protected] or shuster 5.15 amplifiers and...
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Dr. Un-ki Yang
Particle Physics Group
[email protected] or Shuster 5.15
Amplifiers and Feedback: 3Amplifiers and Feedback: 3
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Web page for Amp & Feedback
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Realistic OP Amplifier: review
Gain is NOT infinite
Gain is NOT constant against frequency
Output response is NOT instantaneous
Output impedance is NOT zero
Input impedance is NOT infinite
Gain drops at high frequency
Bandwidth: a stable range. -3dB
Slew rate: response rate
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Positive Feedback: review
Negative feedback: stabilizes the circuitPositive feedback: saturated output, (+/- 15 V)
thus used for digital electronics.
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Schmitt Trigger: review
V− vs V+ =R1
R1 + R2
VOUT
Two different thresholds V+, depending on Vout: fix a problem for noisy signal
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to t2t1
Schmitt Trigger
Noisy problem is fixed
t V+
t< to V(H)
t >to V(L)
t >t1 V(H)
t >t2 V(L)
threshold V+
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Analogue to Digital conversion (ADC)
Why digitized signal?• Analogue signals can be
distorted and attenuated• Practically impossible to analyze
many analogue channelsQuickTime™ and a
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Analogue to Digital conversion (ADC)
Fast conversion (sampling rate) High accuracy (resolution) Linearity
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ADC
Sampling rate: how often do we need to digitize analogue signal? • good to have a high sampling rate but requires fast
processing• Nyquist rate = use 2 x highest frequency of the signal
Resolution: digitization introduces uncertainty due to a finite step size. • Good resolution: large number of ADC bits: 2n,
but requires fast processing and many chips • Resolution: LSB/2
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Comparator
1 bit ADC: to provide a digital output indicating which of two analog input voltage is larger: the simplest ADC
Properties: very fast (1 clock cycle), very cheap but very poor resolution (~30%)
Vout=G0(V+ - V-)
Vout = +15V if V+ > V-
-15V if V+ < V-
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Flash ADC
For n-bit, use 2n-1 comparators
Each comparator has its own threshold voltage, separated by 1 LSB
The input to all comparators in parallel (one clock cycle)
Output goes to an encoder to get binary format
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3-bit ADC
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Flash ADC
Very fast (basically only one clock cycle): good to process high rate events (10k Hz etc)
Buy requires so many comparators
for high accuracy (good resolution): very expansive. (32-bit : 4X10E9 comparators )
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Slope Converter
Use one integrator and one comparator
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Slope ~ 1/RC* Vin
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Slope Converter ADC
Advantage: good resolution with only two comparators
Does not require precise components: cheap, designed to average out noise
Disadvantage: slow, 2n clock cycles
for n-bits
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If TF is measured for VIN
(T0 is known for VREF )
VIN =TFT0
VREF =NF
N0
VREF
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Successive Approximation ADC
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Use a successive approximation register
Comparator: check Vin vs DAC reference signal ( MSB --> LSB ): binary search
Advantage: faster, only n clock cycles for n-bit
Disadvantage: register for DAC need to be extremely accurate
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DAC (Digital-Analogue-Converter)
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MSB
LSB