As you probably know, some DACs include an R2R network that generates a reference voltage at the output. These resistors are precision resistors. They are often used to switch the current based on the digital value sent to the DAC, thereby generating a voltage at the output amplifier. When using a multiplying DAC, the output amplifier is not integrated. This makes it possible to implement some unusual applications and use the R2R network as a resistor. Are you interested? Today, Thomas Tzscheetzsch, Field Application Engineer Manager at ADI Healthcare customers, explains how "multiplication DACs are used in applications other than DACs." Most DACs operate with a fixed positive reference voltage and the output voltage or current is proportional to the product of the reference voltage and the set digital code. This is not the case for a so-called multiplication digital-to-analog converter (MDAC), whose reference voltage can vary, typically within ±10V. Therefore, the analog output (which is dynamic in both cases) can be affected by the reference voltage and digital code. application With the appropriate wiring, the module can output amplified, attenuated, or inverted signals (relative to the reference signal). Therefore, its application areas include waveform generators, programmable filters, and PGAs (Programmable Gain Amplifiers), as well as many other applications where offset or gain must be adjusted. Figure 1. Circuit with Variable Gain (PGA) Figure 1 shows a 14-bit MDAC AD5453 with a downstream amplifier that can amplify or attenuate signals based on the DAC's programmed digital code. Circuit calculation The output voltage (VOUT) of this circuit is calculated as follows: In addition to the gain and DAC set digital code D, the output voltage is also affected or limited by the op amp supply voltage. In the case shown, the power supply voltage of the ADA4637-1 amplifier is ±15 V and the maximum voltage of ±12 V should be output, so the control range is large enough. The gain is determined by resistors R2 and R3: All resistors (R1 to R3) should have the same temperature coefficient of resistance (TCR), but they do not have to be the same as the TCR of the DAC's internal resistance. Resistor R1 is used to adjust the DAC internal resistance (RFB) based on R2 and R3 and the following relationship: When selecting the resistor, you must ensure that the op amp is still within the operating range at the maximum input voltage (the DAC can handle ±10 V at VREF). It should also be noted that the amplifier's input bias current (IBIAS) is amplified by the resistor (RFB + R2|| R3), which has a considerable effect on the offset voltage. This is why the ADA4637-1 op amp is chosen for its ultralow input bias current and ultralow input offset voltage (according to the data sheet). To prevent instability or so-called ringing of the closed-loop control system, insert a 4.7 pF capacitor between IOUT and RFB; this practice is especially recommended for fast amplifiers. As mentioned earlier, the offset voltage of the amplifier is amplified by the closed-loop gain. When the gain setting external resistance changes and the change value corresponds to a digital step, this value will increase to the desired value, resulting in a differential nonlinearity error. If it is large enough, it may cause the DAC behavior to be non-monotonic. To avoid this effect, it is necessary to choose an amplifier with low offset voltage and low input bias current. Advantages over other circuits In principle, a standard DAC can be used if an external reference is allowed, but there are some major differences between the standard DAC and MDAC. The standard DAC's reference input can only handle unipolar voltages with limited amplitude. In addition to the amplitude, the reference input bandwidth is also very limited. This is represented in the data sheet by the multiplication bandwidth value. Take the AD5664 16-bit DAC as an example. The value is 340 kHz. The reference input of the multiplying DAC can use bipolar voltage, which can also be higher than the supply voltage. The bandwidth is also much higher - the typical bandwidth of the AD5453 is 12 MHz. Conclusion The use of multiplication digital-to-analog converters is not as extensive, but it offers many possibilities. In addition to the high-bandwidth homemade PGA, mobile applications are also very suitable applications because their power requirements are less than 50 μW. Capacitor For Electric Furnace
Capacitor for Electric Furnace, commonly referred to as capacitors, are capacitors, expressed in the letter C.Definition 1: a capacitor, as the name implies, is a "charging vessel", a device that holds charge.Capacitor.Capacitors are one of the most widely used electronic components in electronic equipment. They are widely used in the fields of interleaving, coupling, bypass, filtering, tuning circuit, energy conversion and control.Definition 2: a capacitor consisting of any two conductors (including wires) that are insulated from each other and are very close together.
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