基于atf54143的低噪放LNA的设计100M-500M(4)

100M-500M低噪放设计方案

Active Bias

The main advantage of an active biasing scheme is the ability to hold the drain to source current constant over a wide range of temperature variations. A very inexpensive method of accomplishing this is to use two PNP bipolar transistors arranged in a current mirror configuration as shown in Figure 1. Due to resistors R1 and R3, this circuit is not a true current mirror. However, if the voltage drops across R1 and R3 are kept identical, the current through R3 is stabilized and therefore Ids and Vds are also kept stable. A passive bias network is discussed in Application Note Note that the voltage drop across R1 must be set equal to the voltage drop across R3, but with a current of IR.

V– V(3) R2 ≈R

R2 sets the bias current through Q1.

Vg

(4) R4 ≈c2

R4 sets the gate voltage. Ic2 = Ie2, assuming the hfe of the 1222: 2336EN.pdf

http://www.77cn.com.cn/litweb/pdf/5988-Transistor Q1 is configured with its base and collector tied t

ogether. This acts as a simple PN junction, which helps to t

emperature compensate the emitter-base junction of Q2. To calculate the values of R1, R2, R3, and R4, the following parameters must be known or chosen:Ids is the device drain-to-source current, 60 mA.IR is the reference current for active bias, 2.1 mA.Vdd is the power supply voltage, 5V.

Vds is the device drain-to-source voltage, 3.0V.

Vds' is used in the equations due to the voltage drop across R7 and R8, 3.56V.

Vgs is the typical gate bias, 0.59V.

Vbe1 is the typical base-emitter turn-on voltage for Q1 & Q2, 0.65V.

Therefore, resistor R3, which sets the desired device drain current, is calculated as follows:

(1) R3 ≈V– V

ds c2

where Ialso equal to the reference current IC2 is chosen for stability to be 2.1 mA. This value is

R.

The next three equations are used to calculate the rest of the biasing resistors for Figure 1.

(2) R1 ≈Vdd – V

dsR

4

PNP-transistors is high. Calculated resistor values differ from actual resistors due to available component values.

Table 1. Component Parts List.C1=150 pF 0603 Chip CapacitorC2, C5=68 pF 0603 Chip CapacitorC3, C6=10 nF 0603 Chip CapacitorC4=100 pF 0603 Chip CapacitorC7=1 µF 0603 Chip CapacitorC8=180 pF 0402 Chip CapacitorC9=2.2 pF 0402 Chip CapacitorL1=150 nH TOKO LL1608-FSR15L2=120 nH TOKO LL1608-FSR12R1=680Ω 0603 Chip ResistorR2=1300Ω 0603 Chip ResistorR3=22Ω 0603 Chip ResistorR4=270Ω 0603 Chip ResistorR5=47Ω 0603 Chip ResistorR6=680Ω 0402 Chip ResistorR7, R8=4.7Ω 0603 Chip ResistorQ1, Q2 Phillips Semiconductor BCV62CQ3 Avago Technologies’ ATF-54143

Input and output RF connectors are EF Johnson end-launch

SMA connectors (p.n. 142-0701-881).The numbers associated with the chip capacitors and re-sistors refer to the dimensions of the components: 0402 = 40 x 20 mil, etc.

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