The DC/AC conversion converts the digital quantity D into an analog quantity V proportional thereto, that is, V = R × D, where R is a proportional coefficient. If D is a binary number, expand by weight:
Digital to analog conversion (DC/AC) circuit types are diverse, and most use T-type resistors to decode the network. The working principle of a digital-to-analog conversion circuit with three binary digits is illustrated in detail, as shown in Figure 10-3. In a T-type decoding network, there is a standard power supply VREF. Each bit di (i = 0, 1, 2) of the binary number corresponds to the resistor 2R, and the bidirectional electronic switch Ki is controlled by the binary value di. When di = 0, Ki is grounded, and when di = 1, Ki is turned on. The summing point of the right op amp. The output voltage V is analyzed below.
When D = d2d1d0 = 111, all switches Ki are connected to the amplifier summing point Σ. Since Σ is a virtual point, starting from point A, point D and Σ point are both ground, so:
As can be seen from the above equation, the output voltage is linearly proportional to the binary number D. By adjusting the feedback resistor R0 of the operational amplifier and the reference voltage -VREF, the output voltage V is linearly proportional to the n-bit binary number.
The (R-2R) T-type resistor network and the binary digital control electronic switch are integrated in one chip through their control circuits and form various types of DC/AC chips. There are two ways to output the DC/AC converter chip: current output and voltage output. In actual use, a DC/AC chip with a current output is typically used to add an operational amplifier to achieve a voltage output. From the connection point of view, DC/AC chips can be divided into two categories. One is that the DC/AC chip has a data register and has a data write strobe signal and a chip select signal input line, which can be directly interfaced with the 80C51 single chip microcomputer. As an I/O expansion port for the microcontroller. There are no latches in other types of DC/AC chips. The output signal varies with the input data and therefore cannot be directly connected to the CPU data bus. It must be connected to the system via a parallel port.