# How To Choose RF Inductor for RF Amplifier

#### strahd_von_zarovich

##### Member level 5
Hi Everyone,
I am trying to understand how to choose RF inductor for biasing a RF Amplifier. Some of the amplifiers need inductors and some of them not.
For example in ADL5536 eval board, 470nH inductor is used, but in HMC1114PM5E's eval board no inductor is used. ADL5536's frequency range is between 20MHz-1GHz. HMC1114PM5E's frequency range is 2.7 GHz - 3.3GHz. Is it because 20MHz-1GHz is low so we need 470nH => Z = 2 * 3.14 * 20MHz * 470nH = 59 impedance . For 3 GHz, 3nH gives nearly the same impedance, so maybe trace's inductance is enough?

My second question is should I try to choose inductor value to match 50ohm or higher impedance value is better?

Canberk

#### FvM

##### Super Moderator
Staff member
The bias circuit should have high impedance, at least 10 x Zin at RF.

### strahd_von_zarovich

points: 2

#### vfone

According to HMC1114PM5E datasheet's Fig.7, the circuit use inductors at both drains of the amplifier stages, and most probably they are inside of the chip. At 3.8GHz, and at this relative high output power (10W), these inductors have low nH values. Some manufacturers choose to use the internal bondwires of the chip to build these inductors.
Beware that this is a GaN PA, and have to follow carefully the bias sequence mentioned at page 15, otherwise you lose 84 bucks in one second.

### strahd_von_zarovich

points: 2

#### BigBoss

An choke inductor has to be carefully chosen so that the inductor should satisfy rougly 10x$Z_{0}$ as well as the Self Resonance Frequency of that Inductor should also satify the condition of higher than max. Operating Frequency.