RFHCS362G datasheet(31/54 Pages) MICROCHIP

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DS41189B-page 31

rfHCS362G/362F

6.6

Power Amplifier

The PLL output feeds the power amplifier (PA). The

open-collector differential output (ANT1, ANT2) can be

used to drive a loop antenna directly or converted to

single-ended output via an impenance matching net-

work or balanced-to-unbalanced (balun) transformer.

Pins ANT1 and ANT2 are open-collector outputs and

must be pulled-up to VDDRF through the load.

The differential output of the PA should be matched to

an impedance of 800 to 1000

Ω. Failure to match the

impedance may cause excessive spurious and har-

monic emissions. For more information see Application

Note AN831, Matching Small Loop Antennas to rfPIC

Devices.

The transmit output power can be adjusted in six dis-

crete steps from +2 dBm to -12 dBm by varying the volt-

age (VPS) at the PS/DATAASK pin. Figure 6-5 shows an

example voltage divider network for ASK operation and

Figure 6-6 for FSK operation.

For FSK operation, the PS/DATAASK pin only serves as

a Power Select (PS) pin. An internal 20

μA current

source pushes current through the PS/DATAASK pin

resulting in a voltage drop across resistor R2 at the VPS

level selected for transmitter output power. VPS selects

the PA bias current. Higher transmit power will draw

higher current.

For ASK operation, the function of the PS/DATAASK pin

is to turn the Power Amplifier (PA) on and off. Resistors

R1 and R2 form a voltage divider network to apply volt-

age VPS for the selected transmitter output power. If

maximum transmitter output is desired, the output of a

GP0 pin can be connected directly to PS/DATAASK.

Table 6-6 lists typical values for R1 and R2 for both the

ASK and FSK modes.

FIGURE 6-5:

EXAMPLE ASK POWER

SELECT CIRCUIT

FIGURE 6-6:

EXAMPLE FSK POWER

SELECT CIRCUIT

TABLE 6-6:

POWER SELECT (1)

Note: PS/DATAASK is driven low when RFENIN = 0.

Make sure external circuitry on PS/DATAASK

does not conflict by driving the pin high. The

encoder DATA output works because it is low if

RFENOUT is low

PS/DATAASK

rfHCS362G/362F

DATA IN

VPS

20μA

To power

select

circuitry

PS/DATAASK

rfHCS362G/362F

VPS

20μA

To power

select

circuitry

Transmitter

Output Power

(dBm)

Transmitter

Operating Current

(mA)

Power Select (PS)

Voltage VPS

(Volts) (2)

ASK

FSK

R1 (

Ω)R2 (Ω) (3)

R2 (

Ω)

11.5

≥2.0

2400

4700

≥75K

-1

8.6

1.2

6800

4700

56K

-4

7.3

0.9

11K

4700

47K

-7

6.2

0.7

15K

4700

39K

-10

5.3

0.5

24K

4700

27K

-12

4.8

0.3

43K

4700

15K

-60

<4.8

<0.1

OPEN

4700

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