CN0143

With single-ended signal routing, a single wire from the signal source runs throughout the system to the data acquisition interface. The voltage measured is the difference between the signal and ground. Unfortunately, because ground impedance can never be absolutely zero, "ground" can have different levels in different places. Thus, using single-ended signal traces can introduce errors, especially when the signal traces are long and the ground current contains large digital transients. Single-ended signal traces are sensitive to noise pickup because they act as an antenna, picking up noise from electrical activity. With single-ended inputs, there is no way to distinguish signal from interfering noise, and most ground and noise issues are solved with differential signaling techniques. When using differential signal routing, two signal lines are connected from the signal source to the data acquisition interface, which can solve the above problems caused by single-ended connections. The noise between the transmit and receive ground planes acts as a common-mode signal and is greatly attenuated. Using twisted pairs causes noise pickup to appear as a common-mode signal, which is also significantly attenuated at the receiving end. Differential transmission also has the advantage that the amplitude of the differential signal is twice that of the equivalent single-ended signal, making it more noise immune. The circuit described in this article is a differential driver; it can be adjusted to be used with either a voltage or current output DAC. The driver is based on the AD8042 dual-channel op amp configured as a cross-coupled differential driver. The AD8042 has a rail-to-rail output stage that operates within 30 mV of either supply rail and an input stage that operates within 200 mV of the negative supply (ground in this circuit) and 1 V of the positive supply. Work. In addition, the AD8042's 160 MHz bandwidth and fast settling time make it an ideal choice as an output driver. The voltage output DAC is a 12-bit AD5620 from the nanoDAC® series. It contains a 5 ppm/°C on-chip voltage reference and is available in an 8-pin SOT-23 or MSOP package. The current output DAC is a 12-bit AD5443, which is available in a 10-pin MSOP package. These two circuits represent a cost-effective, low-power, small-footprint solution for applications that generate differential signals from industrial CMOS DACs. Both circuits operate from a single +5 V supply.