CDMA or WCDMA PA TX sequence

[vfone]

wcdma duty cycle

Hi
Does anybody know the TX sequence of the PA in CDMA or WCDMA?
I am interested about sequence of Vcc, TX_ON and RF input (wich is coming first). Also if PA TX_ON is ON all the time during the call.

regards

 

[syncmaster]

cdma duty cycle

I think the vcc is always on, TX_ON is determined by baseband, i.e, when transmit TX_ON is enable. the rf signal is transmitted when TX is ON.

 

[jon2000]

wcdma pa

For CDMA cell phone, normally PA_VCC is always on, but TX_VCC is not always ON. According to Qualcomm, two signals, IDLE_N and PA_ON control the power states of the TX circuitry. PA_ON is used to turn on/off the PA and IDLE_N to turn on/off other TX circuitry. PA_ON goes to HIGH whenever IDLE_N is HIGH. IDLE_N controls TX_VCC.

So basically the TX on sequence is IDLE_N, PA_ON and then TX signal.

 

[vfone]

jon2000 thanks and sorry for the delay; do you know where I can find the Qualcomm document that you are talking about?

tnx

 

[toonafishy]

Not quite. IDLE_N is actually used to control the linearity of the receiver depending if the transmitter is on or off. If the transmitter is off, then the receiver will not suffer from cross modulation (single tone desense). So you can run lower current into the receiver and save battery life. If the transmitter is on, then the receiver will suffer from cross modulation and higher linearity is needed, hence more cruent is fed into the receiver to improve the linearity.
PA_ON is a high speed control line that turns the transmitter stages on and off. If the transmitter is running less than full rate, this line pulses the transmitter on/off for the 1/2, 1/4 or 1/8th duty cycle.
When your handset is just sitting idle, VCC_TX is turned off. When you place a call, VCC_TX is turned on, then PA_ON activates all the transmitter stages. Then the IQ datastream starts from the baseband through the transmttter chain.

 

[vfone]

toonafishy sorry but you confuse me a little. You said that in CDMA mobile the PA_ON is going on/off during a call, for different duty cycles? I knew that is going on/off during DTX, witch anyway is not very well implemented in CDMA (as in GSM). Is hard to believe that is so fast as you said. Don’t forget the PA bias shall be settling before RF is coming.
I do have the same question as above. Do you know where I can find the Qualcomm document that reflect this sequence?
thanks

 

[toonafishy]

Yes it is true. When the voice duty cycle is less than 100%, the transmitter duty cycle also drops. The only reason for this is to save battery power and the only way to do this is to actually shut the transmitter down. The transmitter and the control line respond in less than 10 microseconds. If you are on a call and stop talking into the phone, the transmitter will switch to 1/8 rate mode, that is it is on 1/8 of the time and off 7/8 of the time. This is easily seen on a spectrum analyzer.
You don't need a Qcomm document for this. It is one of the standard test the handset must pass in the IS95/IS98 standard. Just look there.