SAR-ADC 教程之三

AC motor
9
Training 10
The motor control loop is regulated with 16kHz. For the regulation, the current at the phase and the position of the motor needs to be measured. From time to time the DC link voltage and the temperature need to be monitored. An analog input voltage might be used to set the speed of interest. Which is the right ADC architecture: a) For the current measurement, which is measured as voltage across a shunt resistor b) For the DC link voltage measurement, which is also at a high-voltage potential c) For the temperature d) For the analog input voltage 10
16 14 12 8 ENOB (bit) ENOB (bit) 10 sinc3 8 6 4 2 2 0 1 10 OSR 100 1000 0 0 2 4 6 8 10 settling time (us) sinc2 sinc sinc3 6 sinc2 sinc1 4 12 10
6
Training 10
One for over-current protection in failure modes, where the over-current needs to be detected within 5μs. Which filter should be chosen (order and OSR) and what is the maximum resolution. The second filter should generate a 12bit value. Which filter should be used (order and OSR).
Order: m = sinc 3 OSR = 64
8
Training 10
4. Application Motor Control: Which is the right ADC type
AC supply
Link Sensor
IGBTs
Current Sensor IU Current Sensor IV Current Sensor IW
Training 10
a) For the current measurement, which is measured as voltage across a shunt resistor The voltage across the shunt resistor has to be small to keep the power loss small The interface needs to be galvanically isolated
The second filter should generate a 12bit value. Which filter should be used (order and OSR).
16 14 12 10 sinc3 8 6 4 2 0 1 10 OSR 100 1000 sinc2 sinc
ENOB (bit)
Analog Input
DC Link Voltage Analog Input Voltage Positioning Sensor at load (Encoder)
Current IU Current IV Current IW Temperature Positioning Sensor at motor Resolver or Encoder
ADC Architecture: Delta-Sigma Modulator - High resolution even at a low input voltage - 2 wire interface (clock, data)
11
Training 10
b) For the DC link voltage measurement, which is also at a high-voltage potential 8-10bit resolution is enough The interface might require galvanic isolation
17
Training 10
Weight Scale: 17bit (noise, INL) Slow speed
ADC Architecture: Delta-Sigma ADC
18
Training 10
6. Touch screen: The X and the Y coordinates have to be measured of the finger position on a screen. A multiplexer is used to connect either the X or the Y coordinate to one ADC input. Human motion is slow, so that 100kSPS is more than enough. The resolution should be higher than 10bits. What are the important specifications and what is the best ADC architecture.
ADC Architecture: integrated ADC in μ−controller
13
Training 10
d) For the analog input voltage: 12-16bit accuracy (noise, INL) 16kSPS conversion rate +/-10V signals
19
Training 10
Touch Screen: 10-12bit 100kHz Snapshot, multi-channel
ADC Architecture: SAR ADC
20
Training 10
7. A/V Amplifiers include an ADC and a DAC, so that the audio signal can be digitized first, then processed with a DSP and finally converted back into the analog domain to drive the loudspeakers. What are the important specifications and what is the right type of ADC.
12 10
Order: m = sinc 3
sinc3 sinc2 sinc1
8 ENOB (bit)
6
4
OSR = 5us/(100ns·3) OSR = 16 Resolution ENOB = 7.8bit
7
2
0 0 2 4 6 8 10 settling time (us)
Training 10
Signal period 360º elect.
A
ϕ1
ϕ2
PA NA
MA
B
PB NB
MB
15
Training 10
e) For the analog input voltage: 10-12bit accuracy (DNL) Snapshot on external hold signal Up to 500kHz signals
4
Training 10
5
Training 10
3. A delta-sigma modulator with 10MHz clock shows the performance below. It is used for the current measurement in a motor control application. Two digital filters need to be defined.
ADC Architecture: Delta-Sigma Modulator or integrated ADC in μ−controller if using an isolated sensor
12
Training 10
c) For the temperature: 8bit enough slow speed
2. Calculate the states of an unipolar 5bit SAR converter, which has full-scale range of 4V. The analog input voltage is 2.4V. – How many comparators and buffers are required. – What is the maximum conversion rate at a 20MHz clock, what is the throughput rate.
ADC Architecture: Delta Sigma or SAR ADC Alternative for a-e): multi-channel SAR ADC
14
Training 10
e) The angle could be measured with an optical encoder. If the motor rotates with a maximum of 6000rpm and the encoder has 2000 stripes, then the sine wave, which needs to be monitored, reaches 200kHz.
2
Training 10
4x 2bit ADC: 4x 3 comparators + 3 buffer = 15 active circuits Conversion rate = Clock rate (20MHz) Throughput rate= fclk/4=5MHz
3
Training 10
Presented by Frank Ohnhäuser, Texas Instruments
Training 10: Analog-to-Digital Converter (ADC) Converter Types
1
Training 10
1. Design an 8 bit Pipeline ADC with 2bit resolution per stage. – How many comparators and buffers are required. – What is the maximum conversion rate at a 20MHz clock, what is the throughput rate.
ADC Architecture: SAR ADC
16
Training 10
5. Industrial weight Scale The scale should be accurate to 0.5kg, over a range of 0 to 40tons. What are the important specifications and what is the best ADC architecture.
Filter for over-current protection in failure modes, where the over-current needs to be detected within 5μs. Which filter should be chosen (order and OSR) and what is the maximum resolution.