Hi, about harmonic question?

[mckinson]

When I added a matching network at DCS band ,the GSM 2nd (about 1.8048G) harmonic get very bad ,very close to the limit -30dbm. But I removed the added the matching , the harmonic getting better about -45dbm . The matching network can improve the phase error , power roll off , switching spectrum , power time for DCS band . So I don't want to remove the matching network .
Could someone please give me some advice for that?
Best regards!!!

 

[sergio mariotti]

I mean you are speaking about an amplifier.
If it's correct, and if you don't want place a filter, you my think to design a "balanced" amplifer.
2 identical stages supplied by a 90° splitter.
Since the 90° splitter is relatively insensitive to Ampli mismatch, you can now add the network you designed, the degradation should be now limited and accettable.

 

[vfone]

You have a crossband-isolaton issue there. This could be an internal problem in the dual-band PA. I’ve seen dual-band PA’s from different manufacturers that in GSM900 mode the level of the 2nd harmonic was very low at GSM port (-40dBm), but at DCS port the same GSM900 2nd harmonic was very strong (-5dBm).
For this path, between DCS output and antenna connector, you have just the isolation of the T/R switch (~25dB) which can help you, so finally you get in GSM900 mode at antenna connector –30dBm of 2nd harmonic. This because the internal crossband-isolation of the PA is not very good.
If you use an old PA with LPF external, this could be a layout problem that generates this cross-isolation issue.
regards

 

[IICCEE]

Because the Device is under nonlinear operation state.So there is homonic.

I suggest you use the lpf behavior match circuit ot Band pass circuit type.

That is a ref:

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 52, NO. 3, MARCH 2004 927
Amplifier Linearization Using Compact Microstrip
Resonant Cell—Theory and Experiment
Tsz Yin Yum, Student Member, IEEE, Quan Xue, Member, IEEE, and Chi Hou Chan, Fellow, IEEE

Abstract—This paper presents a novel technique for reducing
the intermodulation distortions (IMDs) in power amplifiers. In this
method, both second- and third-harmonic components generated
by the transistor are reflected back simultaneously by the compact
microstrip resonant cell (CMRC) at the input port with proper
phases to mix with the fundamental signal for the reduction of
IMDs. A rigorous mathematical analysis on the effectiveness of
multiharmonic reflections has been formulated and derived using
the Volterra series. Moreover, the delay mismatch factor of the
proposed method is analytically studied and the result shows that
a better tolerance to the delay error can be achieved by using
CMRC circuitry. Standard two-tone test measurements reveal 32-
and 22-dB reductions for the third-order IMD and fifth-order
IMD, respectively, without affecting the fundamental signal at
2.45 GHz. Meanwhile, the proposed approach gives a peak power
added efficiency of 53% with 11.5 dB transducer gain and 15 dBm
output power for a single-stage SiGe bipolar junction transistor.
The adjacent channel power ratio (ACPR) is 55 dBc for a data
rate of 384-kb/s quadrature phase shift keyed modulated signal
with 2-MHz spanning bandwidth, and this ACPR is maintained
for a broad range of output power level.
Index Terms—Amplifiers, compact microstrip resonant cell
(CMRC), harmonics suppression, intermodulation, linearization.

 

[IICCEE]

Resonant Cell is just a bpf behavior.

 

[activewei]

Hi mckinson: Have you found any solution for the problem raised? and did u try out the suggestion given by the members? I am keen to know the result....

 

[mckinson]

I've found the GSM 2n harmonic is just only relative to inductor (2.7n ) of the matching network .Because we removed the capacitor(1p ), the impedance of the PA output and FEM input must be changed , but
the GSM 2nd harmonic still is very big , the same as before .
But when we changed the value of the matching inductor , the harmonic got better . We changed the value of the inductor bigger or smaller , the harmonic had been improved . The harmonic is the worst (-32dbm ) when the inductor value is 2.7n . I don't know what cause this problem . Do you think the inductor cause the the harmonic output getting bigger from PA DCS band or reducing the isolation of FEM dcs band on the GSM transmiter mode ?
Now we have changed the value of the inductor 2.7n to 1n , the capacitor 1p to 0.5p . The GSM
2nd harmonic have been improved 8-10 dbm . The PPE and power rolloff had not much effect , I think the matching network is usefull. ( We have tested 2 pcs mainboard )

 

[activewei]

I've found the GSM 2n harmonic is just only relative to inductor (2.7n ) of the matching network .Because we removed the capacitor(1p ), the impedance of the PA output and FEM input must be changed , but
the GSM 2nd harmonic still is very big , the same as before .
But when we changed the value of the matching inductor , the harmonic got better . We changed the value of the inductor bigger or smaller , the harmonic had been improved . The harmonic is the worst (-32dbm ) when the inductor value is 2.7n . I don't know what cause this problem . Do you think the inductor cause the the harmonic output getting bigger from PA DCS band or reducing the isolation of FEM dcs band on the GSM transmiter mode ?
Now we have changed the value of the inductor 2.7n to 1n , the capacitor 1p to 0.5p . The GSM
2nd harmonic have been improved 8-10 dbm . The PPE and power rolloff had not much effect , I think the matching network is usefull. ( We have tested 2 pcs mainboard )

In fact, based on the capacitor and inductor value, I can conclude that the previous value of LC network has resonat frequency at ~3 GHz (2.7nH and 1 pF). when you change it to 1nH and 0.5 pF, the harmonic is less as the resonant frequency is ~ 7GHz now. Of course it depends on the PA load impedance. The resonant frequency might not be as calculated. BE careful with output matching circuit ...

Did you try isolating the GSM and DCS path??? any improvement on the harmonic rejection?

 

[mckinson]

Hello ,activewei :
I can catch you about the resonant frequency . When I removed the capacitor , I think the resonant frquency must be changed , but the harmonic still is very big , no improvement .
I think the harmonic is just only relatived to the 2.7n inductor .
I disconnected the DCS path , the harmonic got very good .
Do you have any suggestion ?
Best regards !