An Introduction to MMICs
What Is an MMIC?
There are three main circuit technologies used to make RF components: discrete, hybrid and MMIC. MMIC stands for a monolithic microwave integrated circuit. An MMIC is not to be confused with an MIC or microwave integrated circuit. In MICs, active and passive components are attached externally to the circuit. In MMICs, they are part of the circuit board and internal to the chip.
With careful control of feedback networks the MMIC can be designed for a particular input and output impedance. Thus most MMIC’s are designed to have 50 Ohm in and 50 Ohm output over a very wide range of frequencies. This eliminated external impedance matching components resulting in a very simple circuit with extremely wide bandwidth.
MMICs are essentially a complete microwave RF circuit on a chip. An MMIC may be made of transistors or FET’s to make an amplifier or transistors to make a switch or an entire circuit. You can find MMICs for both microwave and millimeter wave applications. MMICs typically cover the microwave frequency range from near audio frequencies to 10 GHz.
What are the most common types of MMICs? What are some of the main uses of MMICs?
A variety of wired MMICs
MMIC Switches
Early MMICs were used as PIN switches. The first multi-octave switch on an MMIC was developed in 1987.
MMIC switches are regularly used for microwave radio and microwave instrumentation applications. They have low insertion loss and high isolation for their given frequency ranges.
T/R Modules
The first MMIC T/R or transmitter and receiver module was developed in 1981; that was a multi-chip component, whereas 1984 saw a T/R module consolidated on a single MMIC.
Frequency Multipliers
A multiplier generates a signal output where the frequency is a multiple or harmonic of the input frequency. MMIC multipliers have lower conversion loss and cover a wide range of frequencies.
For hobby use, the MMIC is simply over driven and a filter selects the desired harmonic, resulting in a simple Frequency Multiplier
MMIC Amplifiers
The first low power amplifier MMIC was created in 1974. A traveling-wave MMIC amplifier was developed in 1981.
MMICs are regularly used in broadband amplifiers for frequencies up to several Gigahertz. The frequency range depends on the chip used. They may be used for power amplification or low noise amplification.
They are preferred for this application since cascading MMICs doesn’t require an external impedance matching network. Another benefit of an MMIC amplifier is that they don’t require a tuned circuit and are usually unconditionally stable.
MMIC amplifiers can be assembled in kits to create very low noise amplifiers suitable for EME and radio astronomy. Very low noise amplifiers assembled from MMICs to receive signals from 50 MHz to over 6000 MHz.
MMIC Attenuators
MMIC attenuators are almost the opposite of an amplifier. An attenuator reduces the power of the power of a signal without altering its wave form.
Microwave Mixing
MMICs have been used for oscillators and microwave signal mixers since the 1970s. MMIC mixers for microwave instrumentation and communications cover a wide frequency range and have low conversion loss.
MMIC Frequency Dividers
MMIC frequency dividers and prescalers are used for high frequency communications, electronic warfare radar systems and microwave instrumentation. MMICs in these applications provide large input power sensitivity and low phase noise. MMIC frequency dividers have been used in collision avoidance systems for cars.
Software Defined Radio
They were used in mobile telephones in the mid-2000s. MMICs are now used in software defined radios, since they cover such a large frequency range. A 144 MHz MMIC transverter can be used to drive microwave band signals from your high frequency band or SDR.
HEMT’s were developed to provide very low noise figures for MMIC receiver applications; later on pseudomorphic high electron mobility transistors (pHEMT) to create extremely efficient power MMIC amplifiers. The compact printed circuit board assembly process means that an MMIC chip can replace an entire amplifier stage made from several discrete components.
Television Signals
When GaAs MMICs started to become commercially available at a low cost in the early 2000s, they started to be used in TV and cable TV tuners. This accounted for about half their usage in 2005. MMICs started to be used for direct broadcast satellite (DBS) receivers around this time. Note that military radar and satellite communications were the original intended usage of MMICs.
The Drawbacks of MMICs
One of the main drawbacks of MMICs is that they’ve traditionally been made using semiconductor manufacturing, raising their cost. Prices have come down over the years. MMIC packages can be sealed hermetically with a base and sidewalls to prevent damage from moisture or corrosion. When this is necessary, the price of each component rises. Fortunately, not all applications require an MMIC to be encapsulated, in which case, they are very cheap.
Summary
MMICs give the hobbyist a simple circuit with good gain, low noise, and low cost. With well over 100 different MMIC’s from a variety of companies, there is a part for most any RF application.
