4 Benefits of Differential Circuits in RF Signal Chain Applications

“When it comes to communication systems, differential circuits always offer better performance than single-ended circuits—they have higher linearity, immunity to common-mode interference signals, and more. Today we will talk about the 4 major advantages of differential circuits in RF signal chain applications.

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When it comes to communication systems, differential circuits always offer better performance than single-ended circuits—they have higher linearity, immunity to common-mode interference signals, and more. Today we will talk about the 4 major advantages of differential circuits in RF signal chain applications.

1. Using a differential circuit can achieve a higher signal amplitude than using a single-ended circuit. Under the same supply voltage, a differential signal can provide twice the amplitude of a single-ended signal, and it can also provide better linearity and SNR performance.

Figure 1: Differential Output Amplitude

2. Differential circuits have good immunity to external EMI and crosstalk from nearby signals. This is because the received useful signal voltage is doubled, and the effect of noise on tightly coupled traces is theoretically the same, and they cancel each other out.

3. EMI generated by differential signals is often lower

This is because changes in signal level (dV/dt or dI/dt) create opposing magnetic fields, which again cancel each other out.

4. Differential signal can suppress even-order harmonics

An example of continuous wave (CW) passing through a gain block is shown below.

When using a single-ended amplifier, as shown in Figure 2, the output can be expressed as Equation 1 and Equation 2.

Figure 2: Single-ended amplifier

When using a differential amplifier, the input and output are shown in Figure 3, expressed as Equation 3, Equation 4, Equation 5, and Equation 6.

Figure 3: Differential Amplifier

Ideally, the output does not have any even-order harmonics, making differential circuits a better choice for communication systems. In fact, the biggest challenge of using differential circuits is to put aside the idea that they are difficult to design, test, and calibrate, and need to carefully observe how to use differential filters.