BAP64Q - Quad PIN diode attenuator

[rk2]

Dear Team,

In datasheet of BAP64Q Application circuit states that shunt diodes are biased with 0.75 Vdc.  But if i try to simulate that circuit i get very poor return loss and attenuation is around 29dB though i very series Pin diode current from 1mA to 100mA.

Since its PI attenuator configuration both series and shunt Impedance need to be varied to attain optimum attenuation.

Kindly suggest a solution to solve this issue.

Regards,

Rohith K 

[rk2]

Dear Team,

Please find application circuit of Quad PIN diode attenuator (BAP64Q) datasheet. When i try to simulate this circuit because of Shunt capacitor C4 and C5 (10nF) input and output return loss was degraded less than -1dB if the shunt diode is biased with 0.75V Vcc. This is eventual because (10nF) capacitor gives 0.7 ohms impedance for my operating condition (460MHz), Hence entire RF power gets reflected which degrades the return loss. 

To resolve this issue i removed the capacitor (C4 and C5) and biased shunt diode Pin 4 and 5 with DC feed inductor. After doing this, circuit return loss improved but insertion loss (attenuation) of the diode was not increased above 1dB after sweeping series Diode bias current  from 1mA to 100mA.

Since it is PI attenuator configuration to attain 30dB attenuation shunt impedance should be around 50 ohms and series impedance should be around 800 ohms. This can be achieved only by enabling shunt diode but it also degrades return loss.

In datasheet of BAP64Q it was mentioned that input return loss is 18dB for F= 1GHz. Can you please share evaluation module part number or actual test circuit to attain 18dB return loss at higher attenuation (38dB).

Regards,

Rohith K

[LPP]

BAP64Q datasheet provides measured performance of the attenuator circuit. Sure, your trouble is related to a simulation issue.
C1, C4 and C5 capacitors provides RF ground at the connection points. They can not be replaced by inductors.

I performed circuit simulation using a model form NXP small signal kit for Keysight ADS. This kit doesn't include BAP64Q and I used BAP64-02 instead. This should not make much difference for this consideration.

The S21 and S11 reports is attached. VCC reference voltage has been tuned to achieve better return loss performance.

Have a great day,
Pavel
TIC
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[rk2]

Dear Pavel,

Thanks for your response and simulation results it will be more helpful if i get diode model BAP64-02.

Also can we generate VCC voltage from resistor divider followed by constant voltage source like emitter follower. will it impact in shunt diode RF performance. Kindly  provide your suggestion on this.

Regards,

Rohith K

[LPP]

The link to the rf small signal models kit for ADS:
https://www.nxp.com/downloads/en/design-support/NXP_Design_Kit_RF_smallsignal.zip

VCC can be generated from a resistor divider. RF performance will not be affected because of the presence of shunt capacitors  C4,C5.

Pavel
NXP TIC

[LPP]

Evaluation board part number is OM7939/BAP64Q,598
I was informed that we have some boards in stock.

Have a great day,
Pavel
TIC
-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!
- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
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[LARMAR]

Hi pavel

Could i use 10v as Vctrl as it has better insersion loss at 3.5 GHz

LARMAR