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.
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about the amplifier AP-10 ,whether is it necessary to add a bias tee to provide the DC Voltage or direct connect the amplifier to DC Voltage ?
What is the voltage tolerance on the -5V supply for a A-2050 amplifier ?
John,
I would guess that the tolerance is pretty loose. Since the current draw varies with input power and frequency of the RF signal, the negative bias should ideally be set to maintain the positive drain current near the recommended 330 mA range. Internally the gate voltage is passed through a resistor to create a voltage divider, so that any voltage noise or variation on the -5V supply will be attenuated by the time it gets to the amplifier chip.
I bought the amplifier A-0010EZP ( connectorized version). I see it has 3 apart from RFin and RFout. I understand that 2 of these 3 pins are for dual bias. What is the third pin for? Is it ground ? What is the recommended square swing at the input if I intend to amplify pulses ?
Shishur,
Good question. The pins are for positive bias, negative bias, and the last one is the ground lug. It attaches to the chassis ground of the part. Always make sure that the amplifier is grounded to your power supply ground before use, or you will see bizarre behavior.