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Questions and Answers
What type of wave is typically used in frequency-based analog-to-digital converters?
What type of wave is typically used in frequency-based analog-to-digital converters?
What component counts the cycles of the frequency signal in an analog-to-digital converter?
What component counts the cycles of the frequency signal in an analog-to-digital converter?
What signal does the computer send to initiate a conversion cycle in a frequency-based ADC?
What signal does the computer send to initiate a conversion cycle in a frequency-based ADC?
Which device is commonly used as a voltage-to-frequency converter in frequency-based ADCs?
Which device is commonly used as a voltage-to-frequency converter in frequency-based ADCs?
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What operation does the one-shot multivibrator perform in an analog-to-digital converter?
What operation does the one-shot multivibrator perform in an analog-to-digital converter?
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What is the typical output voltage range for a bipolar DAC?
What is the typical output voltage range for a bipolar DAC?
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What binary method is common in DACs to represent numbers?
What binary method is common in DACs to represent numbers?
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How does increasing the number of bits affect conversion resolution in a DAC?
How does increasing the number of bits affect conversion resolution in a DAC?
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What is required to establish the output voltage range and resolution of a DAC?
What is required to establish the output voltage range and resolution of a DAC?
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What is the function of a data latch in a DAC?
What is the function of a data latch in a DAC?
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What is the conversion time for a DAC to perform its function?
What is the conversion time for a DAC to perform its function?
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What type of power supply is commonly used for bipolar DACs?
What type of power supply is commonly used for bipolar DACs?
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What is the main principle behind frequency-based converters?
What is the main principle behind frequency-based converters?
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Study Notes
Bipolar DAC
- Bipolar DACs output voltages ranging from positive to negative values, dependent on input binary ranges.
- While computers often use 2's complement for negative numbers, DACs commonly use offset binary.
- In offset binary, the output is centered around half the reference voltage.
- The bipolar DAC relationship equation is: Vout = (N / 2n) * VR - VR / 2
Example Bipolar DAC
- A 10-bit bipolar DAC with a 5V reference,
- Input 04FH (decimal 79) produces -2.11V output.
- Input 2A4H (decimal 676) yields 0.80V output
- Input 512 (decimal) results in a zero output voltage
Conversion Resolution
- Conversion resolution depends on reference voltage and the number of bits.
- Increased bits mean smaller output changes for corresponding binary word changes.
- This leads to better resolution, with smaller output changes between values.
- The smallest possible change in output is calculated as: ΔVout = VR / 2n where:
- ΔVout = smallest possible change in output
- VR = reference voltage
- n = number of bits in the word
Example Resolution Calculation
- For a reference voltage of 10V and a desired output change of 0.04V or less,
- the required number of bits (n) is 8.
DAC Block Diagram
- Digital Input: A parallel binary word with the number of bits defined in the device specifications.
- Power Supply: Bipolar supply between ±12V and ±18V is common. Some DACs use single-supply.
- Reference Supply: Provides the voltage range and resolution for the converter, must be stable and low-ripple. Some integrate internal references.
- Output: Represents the digital input as a voltage.
- Data Latch: Many DACs have an internal latch to hold input data
- Conversion Time: Conversion is virtually instantaneous.
Frequency-Based Converters
- Analog sensor signals can be converted to digital, using sensor signals to produce variable frequency, then counting for a set time
- Counter output measures frequency, representing the sensor signal.
Frequency-Based Converter Diagram/Description
- Sensor signal to frequency converter for proportional frequency (e.g. frequency converted from a square wave).
- The outputted frequency to a counter.
- The device counts the rising/falling edges to identify an entire cycle.
- Counter operation often includes a latch to hold outputs while the counter continues to count.
Frequency-Based Converter Operation Cycle
- Conversion starts with a start-convert signal from the computer.
- The counter resets and triggers a one-shot multivibrator (MV).
- MV produces a defined duration pulse (a start/stop signal for the counter).
- The falling edge signals the conversion's completion (EOC).
- The computer can read the latch value using a RD signal.
Sensor to Frequency Converter (LM 331)
- The LM331 is a common voltage-to-frequency converter.
- Useful for frequency-based ADCs
- Output frequency (fout) is related to input voltage (Vin): fout = Vin / (RLC ⋅ 2.09)
555 Timer
- The 555 timer is for frequency generation dependent on resistance and capacitance values
- Frequency depends on component values: f = 1 / [0.693(RA + 2RB)C]
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Description
Explore the intricacies of Bipolar DACs through this quiz, which covers output voltage ranges, input binary formats, and conversion resolutions. Gain a better understanding of how offset binary operates compared to 2's complement, along with practical examples of voltage outputs. Test your knowledge on key concepts and calculations related to Bipolar Digital-to-Analog Converters.
