9

KESRX05

NOTES (continued)

7. In-band interference rejection for an unmodulated interfering signal at 100kHz low side from the wanted modulated signal at 433.92MHz to

achieve a Bit Error Rate = 0·01. Figure 6 illustrates a suitable test set-up for measuring the interference rejection and selectivity of the receiver.

Wanted signal = 290dBm at 433·92MHz (2kb/. 50% duty cycle), interfering signal = 278dBm at 433·82MHz. (unmodulated). Interference rejection

typically equals +12dBm i.e. in-band interfering signal is 12dBm above the wanted signal level at -90dBm.

8. Actual intermediate frequency determined by choice of crystal and external ceramic filter.

9. For temperatures between 85

°C and 105°C the maximum frequency of operation of the VCO local oscillator must be limited to 470MHz. The

recommended components to limit the maximum free running frequency of the VCO to less than 470MHz, for an operating supply range of

5V65%, are:

values for D!, C11, C18 and L2 given in Tables 5 and 6 cannot be used at temperatures above 85

°C.

10.Sensitivity is defined as the average signal level measured at the input necessary to achieve a bit error rate of 0·01 where the input signal is a

return to zero pulse with an average duty cycle of 50%, 2kb/s data rate. Equivalent to 2109dBm for a 50

Ω input impedance. Does not include the

insertion loss of a front end SAW filter at the R F input but does include the IF filter of 50kHz 3dB bandwidth and a data filter bandwidth of 5kHz.

The results shown in Figure 20 and in the AC Electrical Characteristics (1) on page 7 are with the simple LC circuit L5//C7 tuned correctly to

10·7MHz.

11. This parameter is not 100% tested by production.

Ident

Value

Tolerance

D1

BB833

69%

C11

6·8pF

60·1pF

C18

10pF

60·1pF

L2

39nH

62%

FUNCTIONAL DESCRIPTION

Power Down

The PD pin, a tristate input, provides a 2-stage power down

for the receiver. The receiver is fully operational when the

pin is held high and is fully powered down when the pin is

taken to ground as shown in Table 2.

Status

Pin 25

Receiver powered down

Crystal oscillator running

Receive mode

Low (0V)

PD0

PD1

PD2

Table 2

PD0 = Low

is reduced to its lowest level of ,50

performance after switching to receive mode PD0 to PD2

(Figures 7, 17 and 18). The settling time (time to valid data)

of the receiver can be improved by maintaining the

oscillation of the crystal in PD0 mode by placing a 200K

Ω

resistor in parallel with C14. The addition of this resistor

will increase the current consumption of the receiver by

approximately 20

µA (see Table 1, pin 23).

A non-receiving state with some critical circuits running

is reduced to about 330

µA. When switching to the receive

state, PD1 to PD2 (Figures 7, 17 and 18), data can start to

sensitivity.

PD2 = High

The receiver is fully functional and ready to receive data.

RF Down-Converter

An internal RF amplifier is designed to interface directly to

an antenna or to an input SAW filter with a maximum

insertion loss of 3dB. The RF amplifier gain is about 1 3dB

at 460MHz when matched into the mixer, while the RF

amplifer noise figure is about 4·5dB when fed from a 50

Ω

source. The internal RF amplifier feeds a double balanced

mixer through an external impedance matching circuit,

RFOP to MIXIP.

The AGC circuit monitors the mixer signal output level.

Control is fed back, applying AGC to the RF amplifier to

prevent overloading in the mixer and the generation of

unwanted distortion products. This also has the effect of

reducing the RSSI characteristic slope and extending its

range of operation by more than 20dB at high signal levels

(Figure 13).

The AGC circuit also applies mixer booster current to

improve the linearity of the mixer at high signal levels. This

can be confirmed by monitoring the current consumption

of the receiver with applied RF signal level (Figure 16).

The AGC circuit comes into operation at mixer output

signals greater than approximately 225dBm and reduces

the RF amplifer gain by 6dB at an input signal level of

approximaely 230dBm. Since the AGC operates on the

mixer output signal level then the exact point where the

AGC comes into opera tion depends on the RF amplifer to

mixer matching circuits and RF amplifer gain.

IF Interface

Unlike KESRX01 there is no internal integrated IF filter.

This is to provide a more flexible design and allows the

system designer to use a low IF or high IF up to 15MHz.

Typically, a 10·7MHz ceramic IF filter connected between

IFOUT and IFIN would be used together with an input RF

SAW filter to give very good image channel rejection. The