MICRF008

Micrel

MICRF008

4

July 2003

Note 6.

Sensitivity, a commonly specified receiver parameter, provides an indication of the receiver’s input referred noise, generally input thermal

noise. However, it is possible for a more sensitive receiver to exhibit range performance no better than that of a less sensitive receiver if the

background noise is appreciably higher than the thermal noise. Background noise refers to other interfering signals, such as FM radio

stations, pagers, etc.

A better indicator of achievable receiver range performance is usually given by its selectivity, often stated as intermediate frequency (IF) or

radio frequency (RF) bandwidth, depending on receiver topology. Selectivity is a measure of the rejection by the receiver of ambient noise.

More selective receivers will almost invariably provide better range. Only when the receiver selectivity is so high that most of the noise on the

receiver input is actually thermal will the receiver demonstrate sensitivity-limited performance.

Note 7.

Parameter scales linearly proportional with reference oscillator frequency f

compute new parameter value as the ratio:

f

MHz

3 36MHz

parameter value at 3.36MHz

REFOSC

.

×

()

Note 8.

Spurious reverse isolation represents the spurious components which appear on the RF input pin (ANT) measured into 50

Ω with an input RF

matching network.

Note 9.

Series resistance of the resonator (ceramic or crystal) should be minimized to the extent possible, to ensure oscillation. In case where the

resonator series resistance is too great, the oscillator may oscillate at a diminished peak-to-peak level, or may fail to oscillate entirely. Micrel

recommends that series resistances for ceramic resonators and crystals not exceed 50

Ω and 100Ω respectively.

Note 10. Parameter scales inversely proportional with reference oscillator frequency f

compute new parameter value as the ratio:

3 36MHz

F

MHz

parameter value at 3.36MHz

REFOSC

.

×

()

C

bolic) resistor RSC in the MICRF008 Simplified Block Dia-

gram. The Programmable LPF (Low Pass Filter) is also

illustrated in the MICRF008 Simplified Block Diagram.

SEL0

Programmable LPF

C

Bandwidth (Hz)

Impedance (

0

2400

440k

1

4800

220k

Table 1. Nominal Characteristics

Programmable LPF Bandwidth and C

Impedance

Typical Characteristics

4

6

8

10

12

14

16

18

250

300

350

400

450

500

FREQUENCY (MHz)

Supply Current

vs. Frequency

T

V

0

2

4

6

8

10

12

14

16

18

-40 -20

0

20

40

60

80 100

TEMPERATURE (

°C)

Supply Current

vs. Temperature

f = 315MHz

V