AD7293 datasheet(76/78 Pages) AD

76 / 78 page

AD7293

Data Sheet

Rev. B | Page 76 of 78

Figure 59. Typical Power Amplifier Control Application

DEPLETION MODE AMPLIFIER BIASING AND

PROTECTION

Depletion mode devices (for example, gallium nitride (GaN) or

gallium arsenide (GaAs)) require temperature compensated

gate biasing voltages similar to enhancement mode devices (for

example, laterally diffused metal oxide semiconductor (LDMOS))

to maintain constant quiescent drain current with temperature.

The most important consideration for a depletion mode device

is the biasing sequence. If the gate of a depletion mode device is

at 0 V and the drain voltage is applied, the device may be

damaged by drawing excessive current. It is also likely that a

device may become potentially unstable at lower drain source

voltages. Therefore, decreasing the gate voltage to less than the

pinch off voltage while the drain voltage is being powered on

and off is necessary.

The AD7293 was designed for depletion mode power amplifier

biasing. Bipolar DAC outputs enable negative voltage biasing of

the gate on the depletion mode device. A closed-loop mode

combined with a low temperature drift reference ensures that

the loop is steady over temperature.

The AD7293 works to ensure that instability or destruction of

the depletion mode device is avoided. A PA_ON signal allows

the user the option to control an external PMOS switch to turn

on and off the drain current. This signal is set to the off state on

power-up. Because depletion mode devices require a negative

bias to remain at an acceptable level, and bipolar DACs transmit

on the AVSS supply for proper operation, PA_ON can be triggered

when AVSS exceeds an acceptable level.

In the event of an AVDD voltage supply failure, the bipolar DACs

clamp to the AVSS supply (−5 V), which ensures that the PA

AVDD

VDRIVE

VIN0

VIN1

VIN2

VIN3

UNI-VOUT0

UNI-VOUT1

UNI-VOUT2

UNI-VOUT3

VCLAMP0

DAC

CLAMP

CONTROL

VCLAMP1

BI-VOUT3

BI-VOUT2

BI-VOUT1

BI-VOUT0

AVSS

DACVDD-UNI

DVDD

VREFOUT

REFADC

MUX

PAVDD

PA_ON

VREFIN

D1–

D0–

D1+

D0+

DACVDD-BI

BIPOLAR

DAC

UNIPOLAR

DAC

UNIPOLAR

DAC

UNIPOLAR

DAC

UNIPOLAR

DAC

1.25V

RS3–

RS3+

RS2–

RS2+

RS1–

RS1+

–

BIPOLAR

DAC

BIPOLAR

DAC

BIPOLAR

DAC

RS0–

RS0+

2.5V

PMOS

CONTROL

SPI

INTERFACE

DIGITALI/Os

ALERT AND LIMIT

REGISTERS

CONTROL

LOGIC

AD7293

RESET

LOGIC

BI-VOUT0MON

BI-VOUT1MON

BI-VOUT2MON

BI-VOUT3MON

FILTER

RFOUT

GaN

RFIN

RSENSE

FILTER

RFOUT

GaN

RFIN

RSENSE

FILTER

RFOUT

GaN

RFIN

RSENSE

FILTER

RFOUT

GaN

RFIN

RSENSE

VPP

GAIN

CONTROL

GAIN

CONTROL

GAIN

CONTROL

GAIN

CONTROL

Rx POWER

MONITOR

Tx POWER

MONITOR

PRECISION

2.5V

REFERENCE

–

AD7293 Datasheet(PDF) 76 Page - Analog Devices

AD7293 Datasheet(HTML) 76 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

Datasheet Download

Link URL