MICRF506 datasheet(21/28 Pages) MICREL

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Micrel

MICRF506

September 2004

M9999-092904

(408) 955-1690

Transmitter

Power Amplifier

A6..A0

0000000

LNA_by

PA2

PA1

PA0

Sync_en

Mode1

Mode0

Load_en

0000001

Modulation1

Modulation0

‘0’

RSSI_en

LD_en

PF_FC1

PF_FC0

The maximum output power is approximately 10dBm

for a 50_ load. For maximum output power the load

seen by the PA must be resistive. Higher output

power can be obtained by decreasing the load

impedance. However, this will be in conflict with

obtaining impedance match in the LNA. The output

power is programmable in seven steps, with

approximately 3dB between each step. This is

controlled by bits PA2 – PA0. PA2 – PA0 = 1 give

the maximum output power.

The power amplifier can be turned off by setting PA2

– PA0 = 0.

For all other combinations the PA is on and has

maximum power when PA2 – PA0 = 1. The output

power varies about 3dB over power supply 2.0V to

2.5V and about 2dB over temperature -40˚C to

+85˚C. The 2

nd and 3rd harmonic of the PA are as

follows:

nd harmonic:

<-16dBm

rd harmonic:

<-8dBm

To reduce the emission of harmonics, an LC filter

can be added between the ANT pin and the antenna

as shown in Figure 15.

18pF

47pF

15pF

12nH

ANT

Figure 15. LC Filter

This filter is designed for the 434MHz band with

50Ohm terminations. The component values may

have to be tuned to compensate for the layout

parasitics. This filter may also increase the receiver

selectivity.

Frequency Modulation

A6..A0

D6D5

D2D1

0000001

Modulation1

Modulation0

‘0’

RSSI_en

LD_en

PF_FC1

PF_FC0

Modulation1

Modulation0

Modulation Type

Closed loop modulation

using modulator

Not in use

FSK applied using two

sets of dividers

Not in use

Table 11. Modulation Bit Setting

When Modulation1 and Modulation0 is 00, the

modulator needs to be programmed properly, see

“Modulator” section. The modulation signal will now

be applied directly on the phase locked VCO. It is

therefore important that the PLL bandwidth is not too

high, as this will remove the modulation. See “PLL

Filter” section on how to calculate the PLL

components. When using the modulator the

modulation signal is applied to the VCO and

therefore some sort of encoding is needed.

The level of encoding is determined by the PLL loop

filter bandwidth and data rate. Two of the most

common encoding techniques are Manchester

encoding and 3B4B. Other encoding schemes may

also be used.

Manchester encoding is when one bit is encoded in

to a two-bit word and is shown in Table 10. When

using Manchester encoding the maximum overhead

is 100%. When selecting PLL loop filter it is

important to note that the min baud rate is equal to:

baud_min =

baud /s

fbaud_min: The minimum frequency of the baud

rate (Hz)

baud/s: Elements per second (encoded data)

Data

Word

“0”

“10”

“1”

“01”

Table 12. Manchester Encoding

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