Analog to Digital

Comparators are used for many things, but many people want to build analog-to-digital converters using a comparator. Comparators are one basic building block of all ADC architectures. A PICmicro® microcontroller with internal comparators can become an ADC with the application of some software and a minimum of external hardware. In this application note you will be shown how to build a Slope ADC. This ADC has been used with the digital pins on PICmicro microcontrollers for many years. The addition of a comparator to the circuit improves the results and reduces the power consumption.

I had a Basic Stamp project that needed to measure a nominal 12 volt battery, and I wanted a simple solution. This is the simplest I could come up with. The 555 timer will put out positive pulses. The pulse width is inversely proportional to the difference in voltage between the voltage at "ANALOG IN" and the voltage of the 4.7uF capacitor(let's say 2.5 volts). To calibrate this circuit, hook it up to a Basic Stamp measuring positive pulses, and give the circuit a known voltage.

This is an extremely simple ADC for the PC. It connects to the parallel printer port, and runs from a 9V battery. All parts are available from Digi-Key Corporation (1-800-DIGI-KEY), and cost is under $20, including box! Input voltage range is 0 to 5 V. Driver software is in Turbo Pascal. I measured the speed to be roughly 1200 samples/sec on an 8 MHz XT, and 5700/sec on the same PC with a 10 MHz 80286/cache accelerator card turned on.

Fig 1 shows a Mitsubishi M50927-XXXSP/FP 4-bit microcontroller decoding a 4Χ4 keypad using only four digital I/O lines instead of eight. Saving four of a 4-bit µC's precious I/O lines couild be significant. The 4-bit µC's ADC provides the key to the savings. The µC's output lines, F1 through F4, energize the keypad's column lines one at a time via 74HC4049 buffer/ driver. If a user presses a key, the µC's ADC reads an analog voltage coresponding to the row of the pressed key.

The circuit in Fig 1 shows a simple way to operate a 1-MHz, 12-bit ADC (IC1) in DMA mode while alternating between its two analog-input channels. The converter operates continuously, driven by the 1-MHz clock on the S/H input. Tying RD and CS low ensures that data are always present on the ADC's output bus. The outputs of the 74HC74 flip-flop, IC2, change state on the rising edge of the end-of-conversion (EOC) signal.

A PC usually requires a plug-in ADC card to process analog signals. However, with the circuitry in Figure 1, a PC can communicate with an 18-bit ADC through its serial port. The port provides both positive and negative power supplies as well as control signals. IC1 is an 18-bit MAX132 ADC with a serial interface. It requires three input control signals, , DIN, and SCLK, and emits serial data, DOUT, and EOC (end-of-conversion) signals.

Long-distance optical communications and medical equipment, such as CT scanners, can benefit from a fast and accurate data-acquisition system. Optical power systems, such as laser pumps, need to constantly monitor their power levels. In such systems, the incoming laser-power range and the laser control-loop response time are such that the system needs a dynamic range of 90 dB or more and a sampling rate of 1M sample/sec.

This application note uses a timer IC (ICL7555), CMOS logic and discrete transistors to automatically control the conversion the MAX190 12-bit SAR analog-to-digital converter (ADC). The delay between conversions can be programed using a resistor. Logic circuits ensures proper startup when power is applied.

The simple circuit in Fig 1 and an accompanying software routine let you easily substitute a multichannel 12-bit ADC for the 8-bit ADC internal to the 87C752 µC. A single assembly can then implement both the low- and high-performance version of a system. A socket lets you plug in the external ADC when you need it; otherwise, you plug in the network of 10 100V resistors. At power-up, the µC executes a routine that looks for the external converter.

This application note describes a low-cost, high-accuracy watt-hour meter based on the AD7751. The meter described is intended for use in single-phase, two-wire distribution systems. However, the design can easily be adapted to suit specific regional requirements, e.g., in the United States power is usually distributed to residential customers as single-phase, three-wire.

This application note describes techniques for interfacing parallel I/O and serial I/O 8-bit A/D converters to the INS8070 series of microprocessors. A detailed hardware and software interface example is provided for each type of A/D. As examples, the INS8073 is used to interface with the parallel I/O ADC0804, and the INS8072 is used with the serial I/O ADC0833.

Two design features of the ADC0801 series of A/D converters provide for easy solutions to many system design problems. The combination of differential analog voltage inputs and a voltage reference input which can range from near zero to 5VDC are key to these application advantages.

Using a 12-bit-resolution analog-to-digital converter (ADC) does not necessarily mean your system will have 12-bit accuracy. Sometimes, much to the surprise and consternation of engineers, a data-acquisition system will exhibit much lower performance than expected. When this is discovered after the initial prototype run, a mad scramble for a higher-performance ADC ensues, and many hours are spent reworking the design as the deadline for preproduction builds fast approaches.

State of art A/D converters push the limits of performance by definition. This level of performance generally comes at a price: power dissipation, physical size, cost. Balancing this situation is the fact that most systems are limited by the performance of lesser converters, and employing the best converter is generally necessary to get the best overall system performance.

If you have to design a system requiring low power dissipation and high performance data acquisition you would naturally be attracted to the Comlinear CLC949 A/D converter. The CLC949 is a low power, 12 bit A/D Converter capable of achieving 30MSPS sample rates and accurately digitizing signals at high frequencies. At a sample rate of 20MSPS, the CLC949 dissipates very little power: 220mW.

This application note describes the requirements to control the AD7416 via a PIC microcontroller by emulating an I2C bus interface. It will provide code examples and descriptions of both hardware and software. Although this application uses the PIC16F84, it is possible to modify the code to use other microcontrollers from Microchip and other suppliers.

The effect this has on the AD7416/AD7417/AD7418 is that not all of the internal circuitry will have fully switched off. Therefore, applying power before VDD has reached 0 V can cause the AD7416/AD7417/AD7418 to reset into an unknown state.

This application note concentrates on the AD7739 but is also applicable to the AD7732, AD7734, and AD7738.The purpose of this application note is to explore the calibration registers in more detail than is found on the data sheets.

This application note refers only to the AD7739, but is also generally applicable to the AD7732, AD7734, and AD7738. The purpose of this application note is to explain how to optimize the use of these parts in power sensitive applications.

The AD9430-170/210-CMOS evaluation board is designed to accommodate clocking from an external signal source or an on-board XTAL oscillator. The board, as shipped, interfaces with a single-ended 1 V p-p sine wave source applied to SMA J5 on the board. This signal is converted to differential LVPECL levels by an on-board differential receiver, an LVEL16.