Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

PCB layout of Microstrip line BPF question

Status
Not open for further replies.

abc123

Member level 4
Joined
Mar 28, 2002
Messages
74
Helped
3
Reputation
6
Reaction score
1
Trophy points
1,288
Activity points
575
I have a question on the PCB layout of a 2.4GHz tunable combline BPF filter,
It is tunable by changing the voltage of varactor diodes. see the attached picture. There are two possible implementations, Fig.A and Fig.B since the tuning voltage Vtun can not shorted to GND, I need a DC blocking capacitor between the varactor diode and Microstrip lines which is grounded.

the questions is which way is better ? Fig.A or Fig.B

The PCB layout of Fig.A is a little bit messy, Is the series capacitor and diode, may change the length of Microstrip line ?

For the fig.B arrangement what is the DC blocking capacitor should be for varactor diode in 2.4GHz? is the 100pf capacitor good enough to ground the Microstrip line in 2.4GHz frequency?

8_1253144709.jpg
[/img]
 

toonafishy

Full Member level 6
Joined
Jun 18, 2002
Messages
369
Helped
38
Reputation
76
Reaction score
12
Trophy points
1,298
Location
Earth
Activity points
3,187
I prefer A. All your parasitics are in one place at one end of the line. The ground is good. In B, you have parasitics at both ends of the line and the ground is not so good because of the capacitor. You will also need DC blocking capacitors on IN/OUT for B.
For either one, you will need an RF choke in series with the Vtune leads. If you don't the low impedance of the Vtune will short out your RF signal.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top