+2.7V, Single-Supply, Cellular-Band

Linear Power Amplifiers

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13

ence, so the current out of this pin is inversely propor-

tional to the value of the resistor between this pin and

ground. Similarly, the bias current of the first stage in

high-power mode is proportional to the current flowing

out of BIAS1H. The current in the second stage is pro-

portional to the currents out of BIAS2L and BIAS2H for

low- and high-power modes, respectively.

Additionally, these resistors allow for customization of

gain and alternate- and adjacent-channel power ratios.

Increasing the bias current in the first stage increases the

gain and improves alternate-channel power ratio at the

expense of efficiency. Increasing the bias current in the

second stage increases gain at the expense of efficiency

as well as adjacent- and alternate-channel power ratios.

The PA bias current can be dynamically adjusted by

summing a current into the bias pin of interest with an

external source such as a DAC. See the MAX2268

Typical Application Circuit for using a voltage DAC and

current setting resistors RTB1 and RTB2. Choosing

RTB1 = R1 and RTB2 = R2 allows current adjustment

between 0mA to double the nominal idle current with

DAC voltages between 0V and 2.4V. The DAC must be

able to source approximately 100µA.

Shutdown Mode

Pull pins 2 and 6 low to place the MAX2267/MAX2268/

MAX2269 into shutdown mode. In this mode, all gain

stages are disabled and supply current drops to 0.5µA.

Applications Information

Increasing Efficiency

The MAX2269 incorporates an additional external

switch to increase efficiency to 17% at +17dBm and to

29% at +27dBm. This increase in efficiency is mainly

due to the additional isolation between the high- and

low-power outputs provided by the external switch.

External Components

The MAX2267/MAX2268/MAX2269 require matching

circuits at their inputs and outputs for operation in a

50

Ω system. The simplified application circuits in

Figures 1, 2, and 3 describe the topology of the circuit-

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

RFIN

L1

PWR

SHDN

L3

C3

C4

L4

RH1

RL2

C1

C12

C11

L2

C2

RH2

C13

C8

C7

RFOUT

C9

C5

RL1

C6

L6

L5

OPTIONAL NOISE-REDUCTION CIRCUIT

MAX2267

Figure 1. MAX2267 Typical Application Circuit