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MAS9142AUA1-T

Power Amplifier Controller (PAC) and 2.8 V, 50 mA LDO Voltage Regulator

Micro Analog Systems Oy 

FUNCTION DESCRIPTION

MAS9142 contains two functionally distinct parts –

the radio frequency power amplifier controller (PAC)

and low-dropout voltage regulator (LDOVR). Both

blocks have separate power lines, which must be

connected together on the system printed circuit

board.

PAC and LDOVR use common thermal protection

and reference voltage generator blocks. There are

three power-down pins on MAS9142: TXEN for PA

controller, VRCTRL for the voltage regulator and

ENREF for the reference generator and thermal

protection block. All power-down pins are pull-down

type and use standard CMOS control voltage levels

and positive logic. The operating modes of MAS9142

are listed in the table below:

VRCTRL

0

0

0

0

1

1

1

1

ENREF

0

0

1

1

0

0

1

1

TXEN

0

1

0

1

0

1

0

1

Mode

Total power-down

PAC on

References 'warm-up'

PAC on

Voltage regulator on

Whole chip on

Voltage regulator on

Whole chip on

The ENREF control pin is included to provide

flexibility: it can be used to switch on the voltage

reference block in a sufficient amount of time before

the regulator or PA controller. When not used, the

two other signals will turn the internal reference

generator on using a logical 'OR' operation. The start-

up time of the reference generator is approximately

10 ms due to the large time constant generated by

the external capacitor connected to CBYPASS pin

and an on-chip resistor.

Power Amplifier Controller (PAC)

The PAC is an operational amplifier based controller

for adjusting the output power of a radio frequency

power amplifier. It takes a voltage input at the RAMP

pin and adjusts the output power of the power

amplifier to a known value. This power value depends

on the external rectification diodes, the directional

coupler and the power amplifier control curve.

The measurement results are obtained using

MAS9142 PA controller, a Hitachi PF08103B RF

power amplifier, an LDC15D type directional coupler

with coupling attenuation of 14 dB and a Schottky

diode pair BAT62 in a feedback loop. The

DA9142.002

4 January, 2002

measurement results are shown in Figure 1. It can

be seen that a ±3σ corridor is approximately 1 dB

even at very low power levels. The measurements

were carried out at room temperature with a supply

voltage of 3.6 V and RF input frequency of 900 MHz.

Measured Pout vs. Vramp of MAS9142

35

0.4

Mean

30

Stdev

0.35

25

0.3

0.25

20

0.2

15

0.15

10

0.1

5

0.05

0

0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

VRAMP, V

Figure 1. MAS9142 measurement results

To achieve a better power supply rejection ratio for

the PAC, the rectification diode biasing is made using

a on-chip 2.8 V voltage reference generator and

biasing resistors. The bias current can vary from

sample to sample, but is constant in the whole

operating temperature and supply voltage range with

accuracy of ±2%.

MAS9142 also guarantees that the radio power is

ramped up and down properly, generating only few

spurious frequency components. For that reason, the

control signal that comes from a D/A converter to the

PAC is first low-pass filtered inside MAS9142 chip.

There are also other RC time constants on the chip,

which help in assuring the stability of the PA control

loop. An optional stabilising capacitor can be

connected between the OAMINUS and OAOUT pins

of MAS9142. In the measurement setup described

above, the additional compensation capacitor was not

used.

Low-Dropout Voltage Regulator (LDOVR)

The LDOVR is a high performance, low dropout

voltage regulator including short circuit current and

thermal protection. The circuit also contains

necessary reference voltage and current generators,

so minimum number of external components are

required.

6 (11)

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