Continue to Site

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.

Register Log in

Why are two different impedance values given in this datasheet?

Status
Not open for further replies.
E

ElectricalEngineer

Junior Member level 1
Joined
Dec 29, 2010
Messages
15
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,491
In this datasheet two different impedance values are given for the same frequency. I was hoping someone could explain why this is?

MRFE6VS25LR5 Datasheet [PDF]

Page 15, and Page 22.

On page 15:

VDD = 50V, IDQ = 25mA, Pout = 25W CW
30MHz Zsource:44.9-j2.5, Zload=47.7-j6.1

"Zsource = Test circuit impedance as measured from gate to ground"

On page 22:
VDD = 50V, IDQ = 25mA, Pout = 25W CW
30MHz Zsource:7.2 - j0.6 Zload=15.4 + j8.1
"Zsource = Test circuit impedance as measured from gate to ground"

Both of them have the same measurement technique, and are a the same VDD/IDQ/Pout levels.
 

The parameter is test circuit impedance, describing two different test circuits. As expectable, different circuits have different impedances.

You may want to read the datasheet more thoroughly to understand the purpose of having different test circuits. At first sight, they are targeting to completely different frequency bands. In one case, 30 MHz is the upper end, in the other the lower.

Although you'll ideally want the same matching for 30 MHz with both circuits, realize that matching circuits can't be ideal and involve an impedance error.
 

Yes, but the Zo for higher band is 25 Ohms. The reference plane of the test circuit is not same anymore, hence different impedance values.
 

ElectricalEngineer said:
In this datasheet two different impedance values are given for the same frequency. I was hoping someone could explain why this is?

MRFE6VS25LR5 Datasheet [PDF]

Page 15, and Page 22.

On page 15:

VDD = 50V, IDQ = 25mA, Pout = 25W CW
30MHz Zsource:44.9-j2.5, Zload=47.7-j6.1

"Zsource = Test circuit impedance as measured from gate to ground"

On page 22:
VDD = 50V, IDQ = 25mA, Pout = 25W CW
30MHz Zsource:7.2 - j0.6 Zload=15.4 + j8.1
"Zsource = Test circuit impedance as measured from gate to ground"

Both of them have the same measurement technique, and are a the same VDD/IDQ/Pout levels.
Click to expand...

Because these Impedances have been extracted from real Matching Circuits, not measured.The matching circuits are different and have been optimized regarding to mid-band frequency, therefore they are quite different.I guess, Input Impedances of this transistor drops radically therefore there are difference.It also depends on designer's choice.If the designer has choosen high-end of the band, ( because of roll-off effect ) the impedances can be found pretty diferent.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top