The Science of Sound is widely recognized as the leading textbook in the field. Convert currency. The Science of Sound, 3rd Edition Hardcover Thomas D. Richard Moore and Paul A. The Springer Handbook of Acoustics is also in his 2nd edition an unparalleled modern handbook reflecting this richly interdisciplinary nature edited by one of the acknowledged masters in the field, Thomas Rossing. Researchers and students benefit from the comprehensive contents.
Rossing completed his B.A. At Luther College in 1950, his M.S. At Iowa State University in 1954. His dissertation was in the field of molecular physics. After graduating, he went into industrial research, and from there, he went to teaching.
Currently, he is a professor at Northern Illinois University.Professor Rossing has published more than 200 papers and ten books. He is a Fellow of the Acoustical Society of America and of the American Association for the Advancement of Science. He has held about a dozen research positions other than at his home institution-in national laboratories, in research universities, and in several other countries. The Acoustical Society of America awarded him the Silver Medal in Musical Acoustics.
Dogan Ibrahim, in, 2019 8.27 Using the Digital-to-Analog ConverterDigital-to-analog converter (DAC) modules are important parts of microcontrollers as they enable analog signals to be output from the microcontroller. DACs receive digital signals and convert them into analog form. For example, we can generate and send out various waveforms through the DAC module, or we can filter an analog signal and send out the filtered waveform through the DAC module.Just like the ADCs, the resolution of a DAC depends on the number of bits used in the conversion process. Also, as with the ADCs, DACs also have reference voltages and the output analog voltage depends on the value of this reference voltage.
For example, with a 12-bit (4096 steps) DAC and with a reference voltage of + 3.3 V, each DAC step corresponds to 3300/4096 = 0.805 mV. Thus, for example, the 12-bit digital value of “1011 0000 1111” (i.e., decimal 2831) corresponds to 2831 × 0.805 = 2.278 V.The STM32F411RET6 processor on the Nucleo-F411RE development board has no built-in DAC modules. Most other Nucleo boards, however, have one or more DAC modules. For example, the Nucleo-L476RG development board has two built-in DAC modules. Because the DAC is an important part of a microcontroller, we shall see in this section how to use a DAC module by programming the Nucleo-L476RG board using Mbed. There are two 12-bit DACs on the Nucleo-L476RG development board, available at pins PA4 and PA5.
A DAC port is configured using the statement AnalogOut. The following functions are available with the AnalogOut:write: This function sends out analog data to the specified analog pin. Valid values are 0.0–1.0 where 0.0 corresponds to 0 V and 1.0 corresponds to + 3.3 V.writeu16: This function sends out analog data to the specified analog pin. Valid values are 0–65,535, where 0 corresponds to 0 V and 65,535 corresponds to + 3.3 V.read: This function returns the analog voltage sent to the specified analog pin. Returned values are 0.0–1.0.As an example, analog output of 0.5 corresponds to 0.5 × 3.3 V = 1.65 V. A voltage source multiplying DACNearly all commonly used DACs are ZOH devices and therefore image-rejection filters are needed.
The settling time of multiplying DACs is short because the conversion is done in parallel. 2.6.2 Bit stream DACA disadvantage of multiplying DAC is that the most significant bit (MSB) must be very accurate.
This accuracy will be required for the whole range of temperatures specified for the device. Furthermore, it is to be consistent over time.For an 8-bit DAC, the MSB must be accurate to one part in 2 8 = 256. The MSB of a 16-bit DAC will need to be accurate to one part in 2 16 = 65 536. Otherwise, some of the least significant bits will be rendered useless and the true resolution of the DAC will diminish. Maintaining voltage and current sources to this level of accuracy is not easy. One way of overcoming this problem is to use bit stream conversion techniques.
The concept is similar to sigma-delta ADCs. In bit stream DACs, a substantially higher sampling frequency is used in exchange for a smaller number of quantization levels. Figure 2.39 shows the input oversampling stage of a particular bit stream DAC.
The input to this stage is an n-bit digital input sampled at a frequency f a and the output is an ( n−2) bit data sequence sampled at 4 f a. The difference between the current digital input and the digital output is computed. The integrator is digital and simply adds the previous value to the present one. The output of the integrator is quantized into ( n−2) bits by truncating the two least significant bits. This loss of resolution is compensated for by the feedback of the output to the input and also the fact that this operation is performed four times for each digital input sample.
In general, for an n-bit input and a q-bit quantizer, the oversampling frequency will need to be 2 n-q times the original sampling rate. For some practical DACs, the output of this oversampling stage is a 1-bit representation of the input signal. This bit stream if plotted against time and with sample points joined together, is equivalent to a pulse density modulated (PDM) waveform as shown in Figure 2.40.
This bit stream is converted to an analog signal by a 1-bit DAC and subsequently low-pass filtered. A pulse density modulated waveformOwing to the fact that the original digital signal is being requantized into a small number of levels, the output can sometimes be ‘stuck’ at an incorrect value. This happens most often when there is a long sequence of the same input value. This ‘hang-up’ will persist until the next change in input value. The result of this ‘hang-up’ is that the output will have a substantially different DC (or average) value to that of the input signal.To overcome this problem, a dithering signal can be added.
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The effect of dithering has been discussed in section 2.3.4. In this case, dithering lowers the probability of long sequences of any one value.A further problem with bit stream techniques is the high oversampling frequency. For instance, if we want to resample a CD quality audio to one bit, then we need a frequency of 2 16 × 44.1 × 10 3 (approximately 3 GHz). This is a very high sampling frequency and is very difficult to implement using present silicon technology. In these cases, 1-bit DAC is not practical. Eventually, the design is a compromise between sampling rate and the number of bits required for the DAC. Bruce Carter, in, 2009 18.1 IntroductionA digital to analog converter, DAC, is a component that takes a digital word and converts it to a corresponding analog voltage.
It has the opposite function of an analog to digital converter. The DAC is capable of producing only a quantized representation of an analog voltage, not an infinite range of output voltages.The application almost always dictates the selection of the DAC, leaving the designer the task of interfacing that converter with the output load.A DAC interfaces with a buffer op amp.
Most DACs are manufactured with a process that is incompatible with op amps. Therefore, the op amp cannot be manufactured on the same IC. It must be external, and its characteristics are an integral part of the conversion process. In most cases, the data sheet makes a recommendation for the selection of a buffer op amp. Follow the recommendation, unless there is a compelling reason not to do so.
Performance can be improved only if you know exactly what op amp specifications need to be optimized.All signal conditioning—low pass filtering, DC offsets, and power stages—should be placed after the recommended op amp buffer. Do not attempt to combine these functions with the buffer unless you are an experienced designer with a good grasp of all of the implications. Bruce Carter, Ron Mancini, in, 2018 15.1 IntroductionA digital-to-analog converter, or D/A, is a component that takes a digital word and converts it to a corresponding analog voltage. It has the opposite function of an A/D converter. The D/A is only capable of producing a quantized representation of an analog voltage, not an infinite range of output voltages.The application will almost always dictate the selection of the D/A converter, leaving the designer the task of interfacing that converter with the output load.A D/A converter interfaces with a buffer op amp. Most D/A converters are manufactured with a process that is incompatible with op amps. Therefore, the op amp cannot be manufactured on the same IC.
It must be external, and its characteristics are an integral part of the conversion process. In most cases, the data sheet will make a recommendation for the selection of a buffer op amp. Follow the recommendation, unless there is a compelling reason not to do so. Performance can be improved only if you know exactly what op amp specifications need to be optimized.Signal conditioning—low-pass filtering, DC offsets, and power stages—should all be placed after the recommended op amp buffer. Do not attempt to combine these functions with the buffer unless you are an experienced designer with a good grasp of all of the implications. Here, V r is the value of the voltage reference, D is the value of the binary input word, n is the number of bits in that word, and V o is the output voltage.
Figure 4.2 shows this equation represented graphically. For each input digital value, there is a corresponding analog output.
It is as if we are creating a voltage staircase with the digital inputs. The number of possible output values is given by 2 n, and the step size by V r/2 n; this is called the resolution.
The maximum possible output value occurs when D = (2 n − 1), so the value of V r as an output is never quite reached. The range of the DAC is the difference between its maximum and minimum output values. For example, a 6-bit DAC will have 64 possible output values; if it has a 3.2 V reference, it will have a resolution (step size) of 50 mV. Most DACs have a simple relationship between their digital input and analog output, with many (including the one inside the LPC1768) applying Eq.
Here, V r is the value of the voltage reference, D is the value of the binary input word, n is the number of bits in that word, and V o is the output voltage. Fig. 4.2 shows this equation represented graphically. For each input digital value, there is a corresponding analog output. It's as if we are creating a voltage staircase with the digital inputs. The number of possible output values is given by 2 n, and the step size by V r/2 n; this is called the resolution. The maximum possible output value occurs when D = (2 n−1), so the value of V r as an output is never quite reached.
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The range of the DAC is the difference between its maximum and minimum output values. For example, a 6-bit DAC will have 64 possible output values; if it has a 3.2 V reference, it will have a resolution (step size) of 50 mV. MARK BAKER, in, 2003 7.1 IntroductionThe digital-to-analog converter (DAC) is perhaps the most ubiquitous type of mixed signal device. Applications for DACs span a wide range, from consumer audio to precision instrumentation, and everything in between. Whether or not you spend much of your career testing DACs, it's still a good idea to know how. There is a terminology and methodology associated with DAC tests that applies to many other areas of mixed signal test. Of course, not all DAC types are tested for all parameters.
Instead, a set of basics tests common to DACs in general are supplemented with specific tests targeted toward the end-use application. DAC Test OverviewA DAC produces a set of analog values that corresponds to the digital input codes. Many DAC designs are actually current output devices, instead of voltage output devices. More often than not, we'll convert the output current to an equivalent voltage level, so the examples in this chapter are based on a voltage output converter.Testing the DC performance of a DAC consists largely of verifying a consistent and linear response.
A typical test setup for testing the DC performance of a DAC device uses the test system signal source to generate a ramp. This ramp signal is routed to the digital pin electronics, which applies voltage level and timing formats. The DAC is driven with sequential digital vectors, causing the DAC analog output to generate a voltage ramp.Efficient analysis of the device response requires that the output voltage be digitized and then processed by the test system's Digital Signal Processor (DSP). The DSP is used to subtract the digitized DAC output from a calculated ideal. The difference between the ideal and actual signal data is analyzed to evaluate DC performance.In order to test the accuracy of each DAC output voltage, the resolution of the test system digitizer must be much greater than the resolution of the DAC under test. If the DAC under test is 12 bits, the digitizer must have an additional 4 bits to achieve a linearity measurement accuracy of 1/16 of the DAC LSB. Measuring to 1/16th of the DAC LSB results does not provide a 5% resolution of each step value.
For linearity testing, the rule of thumb for testing DACs is that the test system digitizer must have a resolution of at least 2 bits greater than the resolution of the DAC, or 1/4 of an LSB. An additional 3 bits of measurement precision is a practical minimum. The DAC0854BIN (National Semiconductor, RS853-315) is a quad 8-bit D/A converter with a serial I/O interface. The pin-out and the internal block diagram are given in Figure 7.4.
It requires a +5V power supply with a typical supply current of 14 mA. Six digital I/O lines (-AU, CLK, -CS, -INT, DI and DO) control all operations of the converter. The DAC0854 contains four D/A converters, each having a reference voltage input (V REF) and an analogue voltage output (V OUT).
The D/A section also has two bias voltage inputs (V BIAS1 and V BIAS2) and a power supply input (AV CC). A 2.65V internal voltage reference (V REF OUT) is provided by the DAC0854.
Pin-out of DAC0854 D/A converter and its internal block diagramThe DAC0854 has two I/O operations: a write and read mode. In the write mode, 8-bit digital data is written to the D/A converter and is converted to an analogue voltage. In the read mode, the data that was written to the D/A converters is read back. Writing or reading can be performed with one D/A converter or with all D/A converters. The mode is set by a control word which is written to the control register. The control word is a stream of bits that is clocked into the DAC0854 from the Data Input. The bit functions of the word are given below.
When accessing to a single DAC channel, A0 and A1 select one of the four channels. When the global operation is selected (bit 3 = 1), bit 5 and bit 6 are omitted (the control word only has four bits). When the update bit is 1, the input digital data is converted into an analogue voltage at the rising edge of -CS.AU (asynchronous update) should be pulled high or left open. All operations are initiated by a low-going transition on -CS.
Then the bits of the control word are placed on the DI pins. Each bit is clocked into the DAC at the rising edge of the clock. Figure 7.5 gives the timing sequence of the write operation.
An experimental circuit using the Centronic experimental board is shown in Figure 7.6. D1, D2 and D3 on the board are connected to the CLK, -CS and DI. S1 terminal is connected to the DO. The software driver is written in Turbo Pascal 6. ALLDAC (DATA:byte) writes DATA to all D/A converters. ONEDAC(ADDRESS, DATA: byte) writes DATA to one D/A converter specified by the ADDRESS.
The program causes the DAC0854 to generate a saw-tooth signal at the fourth D/A channel. The waveform can be observed using an oscilloscope. Figure 364.1.