5GHz Linear Power Amplifiers

6

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Detailed Description

The MAX2840/MAX2841 linear power amplifiers (PAs)

are intended for 5GHz to 6GHz band applications. The

PAs are fully characterized in the 5.15GHz to 5.35GHz

band. The PAs consist of two driver stages and an out-

put stage. The ICs also feature an integrated power

detector and power shutdown mode.

Dynamic Power Control

The MAX2840/MAX2841 are designed to provide opti-

mum power-added efficiency (PAE) in both high- and

low-power applications. For a +3.3V supply at high-out-

put power level, the output power is typically +18dBm

(MAX2841) with an idle current of 165mA, or +15dBm

(MAX2840) with an idle current of 120mA. At low-output

power levels, the DC current can be reduced by an

external DAC to improve PAE while maintaining suffi-

cient ACPR performance. This is achieved by using

external resistors connected to the BIAS pin to set the

bias currents of the driver and output stages. See the

Typical Application Circuit for resistor values. Typically,

a DAC voltage of 1.9V gives a 260mA bias current for

the MAX2841, a DAC voltage of 1.6V gives a 155mA

bias current for the MAX2840. Increasing the DAC volt-

age decreases the idle current. Similarly, decreasing

the DAC voltage increases the idle current. Users can

set the desired idle current using only two off-chip 1%

resistors: a shunt resistor (R2) from BIAS to ground and

a series resistor (R1) to the DAC voltage, as shown in

the Typical Application Circuit. Resistor values R1 and

R2 are determined as follows:

[Equation 1]

[Equation 2]

[Equation 3]

[Equation 4]

[Equation 5]

where:

= maximum DAC voltage

= maximum idle current

= DAC voltage

= DAC current

PART

= 1000 for MAX2840, 1600 for MAX2841

If no DAC is used and a constant idle current is

desired, use Equation 4 to determine the resistor values

for a given total bias current. Only R2 is required.

For a DAC capable of sourcing and sinking currents,

the full voltage range of the DAC (typically from 0 to

+3V) can be used. By substituting the desired values of

be easily calculated.

For a DAC capable of sourcing current only, use

Equation 4 to determine the value of resistor R2 for the

desired maximum current. Use Equation 1 to determine

the value of resistor R1 for the desired minimum current.

Pin Description

PIN

NAME

DESCRIPTION

A1

SHDN

Shutdown Input. Drive logic low to place the PA in shutdown mode; drive logic high for normal

operation.

A2, A4, C2,

C4

GND

Ground. Requires a good connection to the circuit board ground plane with multiple vias for lowest

possible inductance and lowest thermal resistance.

A3

DC Supply Voltage. Requires external RF bypass capacitor to ground.

B2

RF_IN

Power Amplifier Input. Requires external DC-blocking capacitor.

B4

RF_OUT

Power Amplifier Output. Requires external DC-blocking capacitor and pullup inductor.

C1

BIAS

Bias Control. Connect two external resistors and DAC block to adjust the bias current.

C3

P_DET

Power Detector Output. This output is a DC voltage indicating the PA output power.