RF3110 Ver la hoja de datos (PDF) - RF Micro Devices

Número de pieza

componentes Descripción

Fabricante

RF3110

TRIPLE-BAND GSM/DCS/PCS POWER AMP MODULE

RF Micro Devices 

RF3110

Where PPA is the output power from the PA, PLOSS the

insertion loss, PIN the input power to the PA and PDC

the delivered DC power.

The RF3110 improves the effective efficiency by mini-

mizing the PLOSS term in the equation. A directional

2

coupler may introduce 0.4dB to 0.5dB loss to the tran-

sit path. To demonstrate the improvement in effective

efficiency consider the following example:

Conventional PA Solution:

PPA = +33 dBm

PIN = +6 dBm

PLOSS = -0.4 dB

VBAT = 3.5 V

IBAT = 1.1 A

ηEFF = 47.2%

RF3110 Solution:

PPA = +33 dBm

PIN = +6 dBm

PLOSS = 0 dB

VBAT = 3.5 V

IBAT = 1.1 A

ηEFF = 51.72%

The RF3110 solution improves effective efficiency 5%.

Output power does not vary due to supply voltage

under normal operating conditions if VRAMP is suffi-

ciently lower than VBATT. By regulating the collector

voltage to the PA the voltage sensitivity is essentially

eliminated. This covers most cases where the PA will

be operated. However, as the battery discharges and

approaches its lower power range the maximum output

power from the PA will also drop slightly. In this case it

is important to also decrease VRAMP to prevent the

power control from inducing switching transients.

These transients occur as a result of the control loop

slowing down and not regulating power in accordance

with VRAMP.

The switching transients due to low battery conditions

are regulated by incorporating the following relation-

ship limiting the maximum VRAMP voltage (Equation 2).

Although no compensation is required for typical bat-

tery conditions, the battery compensation required for

extreme conditions is covered by the relationship in

Equation 4. This should be added to the terminal soft-

ware.

Preliminary

VRAMP

≤

3--

8

⋅

VBATT

+

0.18

(Eq. 4)

Note: Output power is limited by battery voltage. The

relationship in Equation 4 does not limit output power.

Equation 4 limits the VRAMP voltage to correspond with

the battery voltage.

Due to reactive output matches, there are output power

variations across frequency. There are a number of

components that can make the effects greater or less.

The components following the power amplifier often

have insertion loss variation with respect to frequency.

Usually, there is some length of microstrip that follows

the power amplifier. There is also a frequency

response found in directional couplers due to variation

in the coupling factor over frequency, as well as the

sensitivity of the detector diode. Since the RF3110

does not use a directional coupler with a diode detec-

tor, these variations do not occur.

Input impedance variation is found in most GSM power

amplifiers. This is due to a device phenomena where

CBE and CCB (CGS and CSG for a FET) vary over the

bias voltage. The same principle used to make varac-

tors is present in the power amplifiers. The junction

capacitance is a function of the bias across the junc-

tion. This produces input impedance variations as the

Vapc voltage is swept. Although this could present a

problem with frequency pulling the transmit VCO off

frequency, most synthesizer designers use very wide

loop bandwidths to quickly compensate for frequency

variations due to the load variations presented to the

VCO.

The RF3110 presents a very constant load to the VCO.

This is because all stages of the RF3110 are run at

constant bias. As a result, there is constant reactance

at the base emitter and base collector junction of the

input stage to the power amplifier.

2-269

Rev A0 010921

Share Link: