We sell a large product line of packaged amplifiers, primarily for use as LO buffer amplifiers, but that can also be used as general purpose gain blocks. While we don’t design the actual amplifier chips, our expertise is in selecting and packaging these chips to provide easy and guaranteed performance from very low (kHz) to microwave frequencies. Amplifiers can be tricky to deal with, since they generate a large amount of RF power and heat, and use MMIC amplifier chips that can break when not used properly. Here are some guidelines for using Marki Microwave amplifiers:
- Always bias the negative port first: This is because the negative voltage is required to pinch off the gate voltage and ensure that the positive current is limited. If the negative voltage is removed the positive current will flow unimpeded, causing the amplifier to heat up until it burns. This is the easiest way to break a Marki amplifier.
- Only operate the amplifier with a matched load on the output: If the amplifier is run with the output open or shorted, the power has no place to go, and the reflected power may (or may not) burn out the chip. In fact, if you are performing an experiment where the circuit might open or short then measures must be taken to protect the amplifier from the reflection, such as adding an attenuator or circulator.
- Obey the datasheet levels for input power: Providing too much input power will cause the amplifier to clip excessively, and may cause damage.
- Provide some type of heat sinking: Our connectorized amplifiers will operate properly in a room temperature environment with just cabling to remove the heat. If in a heated environment the amplifier will need some way to dissipate heat. For surface mount units make sure that the ground pad has sufficient heat sinking capability to a good chassis or case.
In addition to these precautions to avoid damage, there are some further considerations to optimize performance of the amps:
- For linear operation, input to the amplifier should be below around -15 dBm. This is variable with the gain of the amp, but typically non-linear saturation effects occur around this level. These can be seen with an oscilloscope as clipping of a sine wave, or on a spectrum analyzer as creation of harmonic products (particularly odd harmonics).
- For square wave operation, such as for driving a T3, drive the amplifier at the minimum recommended input power level to ensure clipping and good square wave generation. This can also be seen on an oscilloscope. For T3 optimization the desired goal is to minimize the rise/fall time of the signal.