A hybrid circuit combining monolithic integrated circuits. One of the products (NE-5205) can provide 20dB gain based on the results obtained from the model in the frequency range from DC to 0.66Hz. Another low-cost device (Microcircuit Corporation, MAR-x) provides a gain of 20dB from the 0-26Hz frequency band. Other manufacturers also have many products, some of which have gains up to 30dB and frequencies as high as lSGHz. These devices are unique because their input and output impedances generally match the system impedance of a 50Ω or 75Ω RF circuit.

Monolithic integrated circuits are fabricated on silicon wafers or other semiconductor materials using photolithography or diffusion methods. Both active devices (such as transistors and diodes) and passive devices can be generated in this way. Passive devices, such as on-chip capacitors and resistors, can be produced using thin film technologies of various thicknesses. In the MMIC device, the interconnection between the devices is completed through the on-chip planar transmission line.

Hybrid circuits are more like ordinary discrete circuits, rather than integrated circuits (IC). Passive devices and flat transmission lines are placed on glass, ceramic or other insulating substrates produced by vacuum deposition or other methods. Transistors and unpackaged monolithic integrated circuits are placed on the insulating layer and connected to the substrate circuit through gold or aluminum connecting wires. Since these materials can be used in both HMI products and passive MMIC products, these devices are generally referred to as microwave integrated circuits (MIC), unless there are other classifications.

MIC device has three characteristics. It is simple. As you will see in the following circuit, the MIC circuit usually has only four connections: input, output, ground, and power. Other broadband IC devices usually have 16 pins, most of which are used for bias or capacitor bypass. The second feature is that the applicable frequency range is very wide (from DC to GHz). The third feature is that the input and output impedance changes very stably with frequency.

In most cases, the MIC is very stable because there are many series and parallel negative feedbacks in the circuit. The typical MIC input and output impedance is very close to 50Ω or 75Ω, so there is no need to consider impedance matching when designing the MIC amplifier, which makes it easier to broaden the frequency band. If connected to a suitable system impedance (for example, 50Ω), the standing wave ratio (SWR) of a typical MIC in this frequency band is less than 2:1. It is generally not considered that MIC is a low noise amplifier (LNA), but its noise figure is only 3-8dB. However, some MICs are already LNAs and will become more in the future.

Narrowband and passband amplifiers can also be constructed with MIC. A narrowband amplifier is a special passband amplifier that only resonates at a certain fixed frequency. For example, a 70MHz intermediate frequency amplifier is used in a microwave receiver. Due to the resonance of input and output, such an amplifier will only respond to 70MHz signals.