Why use differential circuits in RF signal chain applications? What are its advantages?

“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 differential circuits can achieve higher signal amplitudes than using single-ended circuits

Differential signals provide twice the amplitude of single-ended signals at the same supply voltage, and it also provides 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 wanted signal voltage is doubled, the effect of noise on tightly coupled traces is theoretically the same, they cancel each other out.

3. Differential signals tend to generate lower EMI as well

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

The following shows an example of continuous wave (CW) passing through a gain block.

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.

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