What is inductive source degeneration?

[btv_murthy]

Dear Sir,
Can you explain me , what is inductive source degenaration ?. I have noticed this while designing low noise amplifier, can you explain it in detail , what is inductive source degeneration.

 

[natnoraa]

take a look at: http://www.nexginrc.org/rftransceiver/files/tutorial2_lnas_tsek03_typed.pdf

pages 11 and 12 for the example. you'll have a bit of understanding

 

[vfone]

A source inductor feedback can rotate S11 of an LNA closer to Γopt, which can help obtaining a minimum Noise Figure and good Input Return Loss simultaneously.
The additional source inductance provides loss-less negative series feedback, and also reduce the overall available gain of the network and can be used in balancing trade-offs between parameters of the LNA as: Gain, IIP3, and stability.
The inductive degeneration does not impact the LNA Noise Figure as much as resistive degeneration does.
At high frequencies this inductance can be achieved with small ustrip lines connected directly to the source of the transistor.

 

[btv_murthy]

vfone Sir,
If we want to have usage of degenerated source inductor. I have doubt , do we need to connect the inductor in series with the gate and source of the transistor as shown in the below attachment of Schematic_Source_Degenerated_Inductor ? . Must we connect the series gate and source inductor for realization of source degenerated inductor?. What type of inductor do we need to connect the series gate and source of the transistor. As mentioned in the given tutorial of natnoraa , Ls may be realized by using "bond wire" and Lg can be implemented by using "spiral/ external inductor"(page no 12 of tutorial, you may have look in the attachment of Usage_of_Source_Degerated_Inductor). What is that "bond wire", what we have to use for bond wire for implementation of Ls in ADS 2009. Can we use spiral/external inductor in the schematic.Can you make it clear.

 

[vfone]

Lg (series gate inductor) is used in narrow band applications to resonate the internal parasitic capacitance Cgs of the transistor, providing good impedance matching at the designed frequency.

ADS has implemented various bond wire models into the simulator engine:

**broken link removed**

 

[btv_murthy]

vfone Sir,
Please answer for degenerated source inductor, what is nothing but the degenerated source inductor . Do we need to connect the external/spiral inductor in series with the source of transistor and bond wire in series with gate of the transistor.I didn't understand, where I need to connect inductor , degenerated source inductor. In ADS , where is the bond wire and spiral/external inductor available, can you make it clear.

 

[vfone]

Regarding the type of inductors that can be used for source degeneration or gate input matching, you can use either type, bond wire or external/spiral inductor for both (source and gate) depending your choice or availability.
For a standard bond wire length vs inductance there is an empirical rule that you can get about 1nH/1mm (up to 2GHz). For frequencies higher than 2GHz have to use complex models built in your simulator.

 

[btv_murthy]

vfone Sir,
We can use bond wire or external/spiral inductor. We can use anyone of these either in series with the gate or in series with the source or in series with the both gate and source. Is it correct, can you make it clear.