# Choose the right components for an MMIC amp

currently I'm studying MMIC amps like this one:

From what I can understand, these MMIC claims to be wideband, and I guess that the operating frequency is given by the components around the MMIC.

Let's take a look to the recommended application circuit for the MAR-8 (datasheet):

First of all, the first important component is the bias resistor: is determined by the given supply voltage for the circuit (eg if Vcc is equal to 7 volt, the bias resistor must have a value of 88.7 ohm; if the Vcc is equal to 12 volt, otherwise, the bias resistor must a have a value of 226 ohm). Another thing that is not clear to me are the values of the two capacitors "Cblock" and the value/presence of the inductor, since, on the above datasheet, the inductor is also stated as optional; I guess that the values of Cblock capacitors and of the inductor will determine the working frequency, am I right?

Well, let's take as example this wideband amp kit: RF wideband amplifier which claims to be able to operate from 0.1 Mhz to 2000 Mhz, and the supply voltage can go from 6 to 12 volt. Is not very clear to me: this kit seems provided with fixed values components: so: how is possible that we can apply a supply voltage from 6 to 12 volt, if there is a bias resistor with a fixed (and unknown) value? And is the same for the inductor and Cblock capacitors: if the inductor and these capacitors will determine a specific frequency, how, this kit (which is provided with fixed value components), would be able to achieve a very wide range of frequencies? Or is just a waste of money, since, maybe, wouldn't be able to work as claimed?

Ok: can someone explain me how to choose Cblock capacitors and the inductor (and why the inductor is stated as optional) to have a MMIC able to effectively work in a wide range of frequencies? And maybe can someone explain/show me a practical example with a schematic, eg, to achieve a MMIC circuit which is able to work from 800 to 1000 Mhz?

Please consider that I am a "newbie" about these subject, so I would appreciate a clear and exhaustive answer.

Many thanks.

• You need to know your source and load impedances, and consider the capacitive impedances in that context.
– user16324
Oct 16, 2015 at 12:52
• What evidence do you have that the "kit" uses the MAR-8 amplifier? Just because something is for sale doesn't mean it's any good (or has been designed properly) and that especially applies to some electronic crap I've seen on ebay. Oct 16, 2015 at 13:38
• You are trying to draw conclusions about a likely crappy circuit on ebay by looking at the data sheet of the transistor that has the same physical form factor with zero evidence that the two are connected. Oct 16, 2015 at 13:45
• Notice how the resistor/Vcc values all provide the same bias? ~3.8V @ 36mA. The part claims to be internally matched to 50ohm. The external components are selected so they don't tune Zin/Zout away from 50ohms at your operating frequency. Oct 21, 2015 at 18:31