MICRF213 datasheet(11/16 Pages) MICREL

11 / 16 page

Micrel, Inc.

MICRF213

May 2007

M9999-052307-A

(408) 944-0800

For best results, the values should always be

optimized for the data pattern used. As the baud rate

increases, the capacitor values decrease. Table 9

shows suggested values for Manchester Encoded

data at 50% duty cycle.

SEL0

JP1

SEL1

JP2

Demod.

(hertz)

Cth

Cagc

Short

1400

100nF

4.7uF

Open

Short

2800

47nF

2.2uF

Short

Open

5300

22nF

1uF

Open

9700

10nF

0.47uF

Table 9. Suggested Cth and Cagc Values

JP3 is a jumper used to configure the digital squelch

function. When it is high, there is no squelch applied

to the digital circuits and the DO (data out) pin yields a

hash signal. When the pin is low, the DO pin activity is

considerably reduced. It will have more or less than

shown in the figure below depending upon the outside

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

obtaining 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 9.

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

DO Pin

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

Other components used include: 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;

and 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 in several devices.

Three other pins need to be discussed as well. 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 families 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

low

Cagc

capacitor value.

DO Pin

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

Making its level close to Vdd (SHDN = 1), the device

is then 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. Crystal vendors suggest that

the data will show up in the DO pin around 1msec

time, and 2msec over the temperature range of the

device. See Figure 10.

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