MOSFET-Only Wideband LNA with Noise Cancelling and Gain Opti(5)

全CMOS噪声抵消和增益优化的宽带LNA

B.Optimization Results

MOS transistor operating in triode region can be modeled C.Simulation Results

In figs. 11-13, we present the simulation results for our MOSFET-only design (initial and optimized) and we compare it with the traditional LNA with resistors.

by a resistor if gds / gm >> 10, otherwise the transistor should be modeled by a resistance in parallel with a current source. The saturation region is reached when ggm is of about the same magnitude as ds. This means that we can increase the incremental load resistance without increasing the DC voltage drop. This allows the gain to be increased with respect to the circuit with true resistors. By simulations we find the boundary between triode and saturation (Fig. 9) and we obtain the gains and noise figure as a function of gds (Fig. 10).

Saturation

Triode

Figure 9. Transistor gm VS gds.

Figure 10. LNA gain optimization project point.

By inspection of Fig. 10 we find that the better operation is before the single stages gain becomes unbalanced (gmS), which occurs before the load transistors reach the ds≈ 3.8 saturation. The circuit parameters are given on table III.

TABLE III. MOSFET PARAMETERS (OPTIMIZED)

D ds m bias

GS

(mA)

( )

(mS)

(µm)

(µm)

(mv)

(mV)

M1

M2 M3 M4

jRy

Figure 11. LNA input impedance.

Figure 12. LNA Gain.

Figure 13. LNA Noise Figure.