why load of LNA is always resistor? not active load.

I've been studying inductorless LNAs.

and in almost every paper, LNA utilizes resistor as a load.

active load(current source load) is better because resistor load limits output voltage swing and active load's output impedance is higher.

why load of LNA is always resistor? not active load.

I do appreciate you to help me.


here's papers i studied

1. A Low Power Inductorless LNA with Double Gm Enhancement in 130 nm CMOS, JSSC2012, Francois Belmas
2. A Wideband Inductorless LNA With Local Feedback and Noise Cancelling for Low-Power Low-Voltage Applications, T-CAS I2010, Hongrui Wang
3. A 2.8-mW Sub-2-dB Noise-Figure Inductorless Wideband CMOS LNA Employing Multiple Feedback, TMTT2011, Ehab Ahmed Sobhy
4. A 0.5 V 3.1 mW Fully Monolithic OOK Receiver for Wireless Local Area Sensor Network, ASSCC2005, Yu-Tso Lin

Maybe to prevent unwanted self-oscillations of some kind?

Because of Drain-Gate and Drain-Substrate capacitance limits the bandwidth and gain.

The resistor is needed to establish the required device current. By adding an inductor in series with it, device frequency response will be affected. It will peak at frequencies close to resonance with appropriate capacitances in the circuit.

because the capacitance of the active load (especially colctor to base ) will hardly limit the bandwidth of the amplifier.
At high frequencies the active load is not anymore a load.

Mandi