Can Anyone Help Me About This Circuit - RF Cafe Forums
Post subject: Can anyone help me about this circuit Posted:
Thu Sep 13, 2007 3:26 am
Sep 13, 2007 2:38 am
I have a problem
with this circuit.
This is a circuit of an ASK Transmitter
module. Circuit works between 4VDC to 12VDC. The module have only
4 pins. GND-DATA-VCC-ANT. I want to understand this circuit deeply
and than make my own circuit. But my circuit must have more output
power and it would be very nice to have that power at 5VDC. How
can I modify this circuit.
Thanks for your help.
Adress of the circuit.
Post subject: Posted: Thu Sep 13, 2007
Joined: Mon Jun 27, 2005 2:02
To me this circuits looks like a Colpitts Oscillator. The capacitors
C5,C6 and L3 form a 180 degrees network and set the oscillation
frequency and the transistor forms the extra 180deg to close the
Capacitors C7, C4 are used for matching to the antenna
Inductors L1, L2 are RF chockes.
The data input
activates the oscillator circuit by causing the NPN conductor to
conduct and this makes the ASK operation, i.e. when there is data
then there will be an output carrier at the antenna port.
If you want to increase the output power you need to connect
an amplifier at the antenna port, this can be a MMIC amplifier or
a discrete amplifier.
It will help if you can provide the
Which gain and output power do you
Hope this helps!
Post subject: Posted: Tue Sep 18, 2007 10:11 am
Joined: Thu Sep 13, 2007 2:38 am
Thanks for your reply.
I have been searching net based
on your reply. Yes, it must be colpitts oscillator.
is no doubt that C4 and C7 are for matching and L2 is RF choke.
But I am not sure with the L1.
Also C5 is generally is optional
in SAW RESONATOR based designs. Please check
One port saw resonator is a 3 terminal device
there is input output and chasis. Generally input and ground is
short circuited. I believe that C5 is for EMC related cap.
With the output power, This circuit has about 10dbm to 12dbm
output power. I need something like 25dbm-40dbm. I hope that reducing
R2 or R1 can solve the problem but I am not sure.
upload a better looking circuit
Post subject: Posted: Tue
Sep 18, 2007 2:28 pm
Joined: Mon Jun
27, 2005 2:02 pm
I am not sure if reducing the value of both resistors will
help you to gain the required power.
The range of output
power which you stated is hugh: 25dBm=0.3W, +40dBm=10W!! This has
a hugh impact on the active device that you will choose as an amplifier.
You should narrow your range and state exactly which output power
Regarding SAW resonator, this works basically
as a high-Q filter and intends to deliver the energy from the tank
to the transistor. Therefore, both pins: IN ans OUT should be used,
and the IN pin to my opinion can't be shorted to GND.
Post subject: Posted: Wed Sep 19, 2007
Joined: Thu Sep 13, 2007 2:38
Sorry!! the values are that I
wrote is in mW range. That means now device has 10-12mW, I need
25-40mW. Basically I would be enough for me to extend range %60-%70.
With SAW resonator I see maybe 10 different saw device manufacturers
datasheet all of them shorts 2 terminals I do not get it. Check