MICRF211 datasheet(12/18 Pages) MICREL

12 / 18 page

Micrel

MICRF211

March 2007

M9999-030107

(408) 944-0800

considerably reduced. It will have more or less than

shown in the figure below depending on the outside

band noise. The penalty for using squelch is a delay in

getting a good signal in the DO pin, that is, it takes

longer for the data to show up. The delay is

dependent upon many factors such as RF signal

intensity, data profile, data rate, CTH and CAGC

capacitor values, and outside band noise. See Figure

8 and Figure 9 below.

Figure 8. Data Out Pin with No Squelch (SQ = 1).

Figure 9. Data Out Pin with Squelch (SQ = 0).

Other components used are C5, which is a decoupling

capacitor for the Vdd line, R4 reserved for future use

and not needed for the evaluation board, R3 for the

shutdown pin (SHDN = 0, device is operation), which

can be removed if that pin is connected to a

microcontroller or an external switch, R1 and R2

which form a voltage divider for the AGC pin. One can

force a voltage in this AGC pin to purposely decrease

the device sensitivity. Special care is needed when

doing this operation, as an external control of the AGC

voltage may vary from lot to lot and may not work the

same for several devices.

Three other pins are worthy of comment. They are the

DO, RSSI, and shut down pins. The DO pin has a

driving capability of 0.4mA. This is good enough for

most of the logic family ICs in the market today. The

RSSI pin provides a transfer function of the RF signal

intensity vs voltage. It is very useful to determine the

signal to noise ratio of the RF link, crude range

estimate

from

the

transmitter

source

and

demodulation, which requires a low CAGC capacitor

value.

The shut down pin (SHDN) is useful to save energy.

When its level close to VDD (SHDN = 1), the device is

not in operation. Its DC current consumption is less

than 1µA (do not forget to remove R3). When toggling

from high to low, there will be a time required for the

device to come to steady state mode, and a time for

data to show up in the DO pin. This time will be

dependent upon many things such as temperature,

crystal used, and if the there is an external oscillator

with faster startup time. Normally, with the crystal

vendors suggested, the data will show up in the DO

around

1msec

time,

and

2msec

over

the

temperature range of the device. When using an

external oscillator or reference oscillator signal, the

time is reduced considerably and can be around

140µsec. See Figures Figure 10 and 11.

Figure 10: Time-to-Good Data After Shut Down Cycle,

Room Temperature.

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