Power Amplifier

Posted on Feb 5, 2014

A simple synthesised 13cm ATV exciter my thoughts turned to what could be used as a power amplifier. The exciter produces about 10mW perhaps enough to drive some sort of MMIC or hybrid amplifier. The problem with 13cm is that at 2. 3 GHz and beyond devices either discreet transistors or amplifiers get very expensive. After researchinga number of

Power Amplifier
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manufacturers and suppliers I eventually came up with an IC amplifier costing about £40 and producing almost a watt, at these frequencies not a bad power to price ratio. The PM2104 manufactured by Pacific Monolithics is a GaAs MMIC amplifier device intended for ISM applications centred on 2. 440 GHz, the device is relatively wide band so covers the whole of the 13cm amateur band. The IC has a gain of 24 dB and runs on a supply of +5V, it also requires two negative bias supplies similar to other gas fet amplifiers. The 2104 is a surface mount device housed in a SOT8 package and heatsinked via its metalised base, it`s pritty tidly so is not recommended for newcomers to surface mount construction techniques. All the clever stuff is done inside the PM2104 IC, fig 1 shows the circuit diagram of the amplifier. The bias supplies and positive supplies are decoupled, some 50R matching resistors and a 33p cap are also required. The device is nominally pre-matched to 50R but a 33p matching cap is needed at the input pin. The device is powered on pins 4 and 8 with 5V. Negative bias is supplied to pins 2 and 5. An ICL7660 DC to DC converter chip is used to generate the negative supply in a similar manner to what is used in some of the Microwave Committee 3cms units. A simple comparator circuit is used to detect the presence of the bias supplies and then switch on the +5V VDD supply to the IC. If the bias voltage fails the IC may be...

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