1、Single-ended signal, Differential signal, and Common-mode signal
  The single-ended signal consists of a signal terminal and a reference terminal of fixed potential, which is typically "ground," as shown in Figure 1.

Figure1 Schematic diagram of single-ended signal

  The differential signal consists of two single-ended signals, which have the same amplitude and opposite polarity relative to a fixed potential reference. This fixed potential reference end is called the common-mode signal, as shown in FIG. 2, and VD is the common-mode voltage.

Figure2 schematic diagram of differential signal

2、The advantages of different signal types
  The biggest advantage of single-ended signal is that the circuit is simple, a signal line and a ground line. The complexity of the circuit can be reduced and the power consumption of the system can be reduced. However, the single-ended signal is susceptible to noise interference, and the difference between the signal ground and the DAQ ground will also lead to errors.
  The advantage of differential signal is that it is more resistant to environmental noise. Especially for the common mode interference, such as the interference introduced by power fluctuations, differential signal can effectively suppress it and is suitable for long-distance transmission. In addition, the maximum swing of the differential signal can reach twice that of the single-ended signal. This is shown in Figure 3.

Figure 3 Differential Signal Swing Amplitude Increase

3、Single-ended, Pseudo-Differential, and Differential ADC
  The single-ended input ADC is shown in FIG. 4. An ADC has a single input and a reference ground (note: a multichannel ADC may have multiple inputs, but each channel is a separate, single-ended input and should not be confused). Simply connect the single-ended signal to the input of the ADC. Different single-ended input ADCs, support unipolar input signals or bipolar input signals.

Figure 4 Single-ended input ADC

  Pseudo-differential input ADC, which has two inputs, but the input signal is also a single-ended signal. The pseudo-difference performs the difference between the single-ended signal and the signal reference level. As shown in FIG. 5, the positive end of the ADC input is connected to the single-ended input signal, and the negative end of the ADC input is connected to the signal reference level. It should be noted that the signal reference level may be the signal ground as in (a) figure, or it may be the reference level of some continuous flow as in (b) figure.
   

Figure 5 Pseudo-differential ADC Connection Method

The two input terminals of the differential ADC, respectively, are connected to the two output nodes of the differential signal, as shown in Figure 6. Differential ADC effectively expands the signal input range.

Figure 6 Differential ADC Connection Method

  According to different requirements, Finetooling Technology has developed a series of high-performance DAQs, which can be flexibly configured for different modes. Support single-stage input signal, bipolar input signal; It also supports different modes such as single-ended, pseudo-differential, differential, so as meet the application needs of various industries to the greatest extent.
  In addition, Finetooling Technology provides a free debugging assistant HWSuit, which offers users with fundamental measurement and analysis functionalities to accelerate the development process of customer’s systems.

Figure 7 Finetooling Technology Series Multi-Functional DAQ

Figure 8 Finetooling technology debugging assistant HWSuit