This paper describes an RF amplifier circuit which is suitable for the frequencies between
10MHz and 500MHz. These kind of amplifiers are called wide band amplifiers.
Wide band amplifiers are used in communication receivers, RF measuring equipment and
tons of other devices. The circuit described here uses a state of the art transistor to get
maximum performance at high frequencies. It can be used as a low noise pre-amplifier
due to his low noise characteristics.
Click here to download the full size of the above Circuit.
This is a classical RF amplifier design. The feedback resistors R3 and R2 define the gain.
By changing the values we can get a higher gain at low frequencies, but this will
influence the overall gain taper of the amplifier. Coil L2 is used to get more gain at high
frequencies. If the value is increased, instability will occur. Dimensions of L2 are:
6 windings, inner diameter is 3mm and wire thickness must be 0.4mm. In the proto type I
used and SMD type for L1, make sure it’s a high Q coil. The transistor, which is used
here, is a wide band transistor with an Ft of 9 GHz. Like in all other RF circuits make
sure that the connections are short as possible.
Supply voltage : +12V
Current : 10mA
Input / output impedance : 50 Ohm
Frequency range : 10MHz 500MHz
Noise figure : 3.5dB typical
IP2 : 110dBuV
IP3 : 105dBuV
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