The difference between the bias tee (Bias-T) and DC Block?

2022-05-28 19:39:30      点击:
The bias tee is essentially a diplexer with extremely low frequency division.

The isolator is a high pass filter whose cut-off frequency is as low as audio frequency and DC frequency.

Bias-t and isolator are both low-frequency filters. Their function is to allow only some required signals and power to pass through, while preventing other irrelevant signals, so as to limit the performance impact on the overall RF / microwave circuit.

DC block is a passive coaxial component. It literally means that the function of the isolator is to prevent DC signals from flowing to RF signals, so as to improve the signal-to-noise ratio and dynamic range of some VLF or broadband systems. It can also be used to isolate and block low-frequency components such as DC and audio during testing. In addition, the isolator can also be used to suppress the modulation leakage of the signal source and eliminate the grounding circuit.

The more conventional application of the isolator is when an energized RF transmission line or "hot" conductor is used. However, the isolator can also be used to isolate the circuit from the ground, DC and audio signals to prevent current from flowing from the circuit node to the ground or generating voltage between the circuit node and the ground. The specific scenario for such applications may be to inject voltage into the source of a shunt field effect transistor (FET), and the grounding point of this source is the grounding housing or fixed fixture of the equipment.

Bias tee, also a passive coaxial component, is mainly used in applications where DC current or voltage needs to be injected into RF circuits. "T" in its name means that the combined shape of three ports is usually T-shaped.

Working principle of a bias tee: to allow DC current and / or voltage to pass through RF devices and block RF and microwave signals on the same line at the same time. The purpose of this design is to inject DC current into the RF circuit without affecting the RF signal passing through the main transmission path. From mobile phone amplifiers to test and measurement equipment, bias tees are widely used. For example, when a transistor or amplifier circuit needs to be injected with a DC signal, and the circuit performance may be affected by the RF component on the signal and power supply line, a bias-t can be connected to limit this negative impact. For another example, when the power supply port of the power probe and the RF signal port are the same port, it is also necessary to access the bias tees. Among bias tees, there is a kind of pulse bias tee, which can minimize the distortion of current, voltage, pulse required by amplifier, and equipment requiring intermittent signal bias and power supply.

There are certain commonalities between bias tee and DC block: when DC signal transmission needs to be carried out simultaneously in the coaxial or microstrip signal path transmitting RF / microwave signals in the RF / microwave circuit, bias-T and isolator need to be connected at the same time. Another scenario is that the DC power supply or bias voltage / current at a certain node in the RF transmission line needs to use both bias tee and isolator, because the downstream transmission after the node may cause destructive results to the whole line.