HT9015 datasheet(16/23 Pages) HOLTEK

16 / 23 page

HT9015

April 10, 2000

Preliminary

· Limiting IF Amplifier, RSSI (Received Signal

Strength Indicator) and RSSI Comparator

The basic function of the IF amp is to boost

the IF signal and to help handle impulse

noise. The IF limiter applies very high gain to

the IF frequency such that the top and bottom

of the waveform are clipped. This helps in re-

ducing AM and noise intercepted upon recep-

tion. The limiting IF amplifier consists of four

differential amplifiers (Figure 6).

· Quadrature detector

Once the signal leaves the IF section, it must

be demodulated so that the baseband signal

can be separated from the IF signal. This is

accomplished by the quadrature detector. A

quadrature detector (Figure 7) uses a 90°

phase shifter (Ci), an L/C tuned circuit, and a

phase comparator to demodulate FM signals.

2nd I F

AM P1

AM P2

AM P3

AM P4

DE C

OF - I N

Q u a d ra t u re

De t e c t o r

(R S S I )

I n t e r nal

LC - T ank

IF - O U T

Figure 6 Limiting IF Amplifier, RSSI and RSSI comparator

V DD

IF _ A M P

B u ffe r

V i

I= I 1 +I 2 ¯

D i f f er ent i a l t o

S i n g l e - E nded C o n v er t e r

LP F

D e m o dul at i o n

S i g nal

f 0 = 47k H z

I L1 ¯

I L2 ¯

I 1 ¯

C i

LC - T ank

V O ¯

I 2 ¯

Figure 7 Quadrature detector

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