In this episode Shahriar explores the world of Delta-Sigma modulators with emphasis on a Delta-Sigma Analog to Digital Converter (ADC). The basic concepts of analog to digital conversion is presented, particularly with respect to quantization noise spectral shape and power density. Next, oversampling ADCs are presented to demonstrate the possibility of increasing SQNR (ENOB) through manipulation of quantization noise spectrum.
Due to the practical limitations of high oversampling ratios, delta-sigma modulations is explored. The principle operation behind delta-sigma ADCs is presented with detailed explanation on noise shaping, filtering and decimation. The signal and noise transfer functions for a 1st order and 2nd order delta-sigma ADC are derived. Finally, as a practical example, a 2nd order delta-sigma ADC based on a 1-bit quantizer is presented. The ADC uses two Miller integrator op-amps, one comparator and a D-Type flip-flop. The complete measurement of this delta-sigma ADC is presented. The impact of over sampling ration, op-amp linearity and input signal bandwidth is presented. The slides for this video can be downloaded from The Signal Path website.
Theory, Design and Characterization of Delta-Sigma Analog to Digital Converters - [Link]
Electronic scales are widely used in kitchens and bathrooms because they can quickly make accurate weight measurements.
A load sensor called a load cell is used for weight measurement. Because the output voltage of this sensor is very small, it is amplified by an operational amplifier (op-amp) and input to an A/D converter. A microcontroller (MCU) converts the signal to weight based on the conversion results of the A/D converter and displays it.
Renesas offers a lineup of microcontroller products for meeting their customers’ needs, such as the RL78/L1x, 78K0/Lx3, and R8C/Lx series with built in LCD driver for designing small and inexpensive models. For highly precise measuring, they offer the 78K0/Lx3, the H8/38086R group, the RX21A group, and other with built-in high precision ΔΣ (delta-sigma) A/D converter.
Renesas MCU for Electronic Scales - [Link]
Build a lab-grade data logger with PIC microcontrolller and a 20-bit delta-sigma converter. Wichit Sirichote writes:
A new design of a lab-grade data logger has been developed using a PIC microcontroller and a 20-bit delta-sigma converter. The data logger provides 8-channel DC inputs and the optional digital inputs. The sampling interval can be programmed from 1min to 1Hr. The device uses a cheap memory card for data storage. In addition, the optional serial port also provides data stream for displaying real-time signal on the terminal.
G5 Data Logger - [Link]
Build a circuit that displays four channels 0-100C using Pt100 as the temperature sensor. Wichit Sirichote writes:
The RTD or the Pt100 is one of the high accuracy temperature sensor for laboratory. Using the high resolution delta-sigma converter, enables designer to use a simple voltage divider circuit for measuring the resistance of the RTD without the need of any DC amplifications. This instrument shows how to use the LTC2420, 20-bit delta-sigma converter and the LM385 reference voltage for measuring four Pt100 sensors and displays on the text LCD.
4-Channel Pt100 Thermometer - [Link]
If you’re interested in how delta-sigma modulators and ADCs work, you should check out this excellent introduction by Uwe Beis: [via]
When looking for an introduction to delta sigma conversion I found that most explanations were from a very theoretical point of view. It took me a while to understand how Delta Sigma converters really work. So I decided to write this introduction for people who prefer circuit diagrams to reading abstract equations.
To understand what I’m talking about you should at least be familiar with:
- Standard analogue techniques (op-amps, comparators etc.)
- Standard digital techniques (latches, binary codes etc.)
- Standard ADCs and DACs (resolution, speed)
- What a low pass filter is (at least an analogue one)
- The sampling theorem (sample frequency > 2 x input bandwidth, alias effects)
Delta sigma converters are different from other converters. Note that I do not make a difference between analogue-to-digital (ADC) and digital-to-analogue converters (DAC). Both are very similar and what is realized in one of them using analogue signal processing circuitry is implemented in the other one using digital signal processing and vice versa. I will explain the delta sigma technique with the analogue-to-analogue delta sigma converter as the first object.
An Introduction to Delta-Sigma Converters – [Link]