ADF7241 datasheet(32/72 Pages) AD

32 / 72 page

ADF7241

Rev. 0 | Page 32 of 72

External PA Interface Modes

•

Mode 0 allows supply to an external circuit to be switched

on or off. This is useful for circuits that have no dedicated

power-down pin and/or have a high power-down current.

•

Mode 1 allows the supply to an external circuit to be switched

on or off. In addition, the PABIOP_ATB4 pin acts as a

programmable current source. A programmable voltage

can be generated if a suitable resistor is connected between

PABIAOP_ATB4 and GND.

•

Mode 2 allows the supply to an external PA circuit to be

switched on or off. In addition, the PABIOP_ATB4 pin acts

as a programmable current sink. A programmable voltage

can be generated if a suitable resistor is connected between

PABIAOP_ATB4 and VDD_BAT.

•

Mode 3 is the same as Mode 1, except that the switch

between PAVSUP_ATB3 and VDD_BAT is open.

•

Mode 4 is the same as Mode 2, except that the switch

between PAVSUP_ATB3 and VDD_BAT is open.

•

Mode 5 is intended for a PA circuit based on a single

external FET. The supply voltage to this FET is controlled

through the PAVSUP_ATB3 pin to ensure a low leakage

current in the power-down state. The bias servo loop

controls the gate bias voltage of the external FET such that

the current through the supply switch is equal to a

reference current. The reference current for the bias servo

loop is generated by the 5-bit reference DAC. In this mode,

the bias servo loop expects the current in the FET to increase

with increasing voltage at the PABIAOP_ATB4 output.

•

Mode 6 is the same as Mode 5, except that the bias servo

loop expects the current in the FET to increase with

decreasing voltage at the PABIAOP_ATB4 output.

LNA

RFIO1P

RFIO1N

RFIO2N

RFIO2P

BALUN

PAVSUP_ATB3

PABIAOP_ATB4

VDD_BAT

TXEN_GP5

ADF7241

GaAs

pHEMT FET

EXTERNAL PA

INTERFACE

CIRCUIT

Figure 39. Typical External PA Applications Circuit

Table 18. PA Interface

Field extpa_bias_mode

Field extpa_bias_en1

VDD_BAT to PAVSUP_ATB3 Switch

Function of Pin PABIAOP_ATB4

Open

Not used

Closed

Not used

Closed

Current source

Closed

Current sink

Open

Current source

Open

Current sink

Closed

Bias current servo output, positive polarity

Closed

Bias current servo output, negative polarity

Reserved

1 Autoenabled when Register ext_ctrl, Field extpa_auto_en = 1.

2 X = don’t care.

PAVSUP_ATB3

PABIAOP_ATB4

ADF7241

DAC

state == TX

CONTROL

LOGIC

SWITCH

VDD_BAT

Figure 40. Details of External PA Interface circuit

ADF7241 Datasheet(PDF) 32 Page - Analog Devices

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