14

µPC2533

2.4

RF AGC Block

Fig. 2-4 RF AGC Block

–

+

–

+

35

36

34

R402

Q402

Q403

Q401

R403

R405

Q405

Q404

R404

R406

D401

R408

Q406

R409

R410

Q407

Q408

R412

AMP.

AMP.

Time

constant

switchover

To RF amplifier

circuit (Fig. 2-1)

Detection

and

addition

circuit

From MIX2

(Fig. 2-3)

From MIX1

(Fig. 2-2)

+

The configuration of the RF AGC is shown in Fig. 2-4. After being detected by the RF AGC detector and added,

the input signal from MIX1 and MIX2 is smoothed by external capacitor of pin 34, and its DC voltage controls the RF

AGC.

RF AGC output controls the PIN diode from pin 36 and controls base voltage of cascade transistor which determines

FET VDS from pin 35. In addition, by detecting sudden fluctuation of pin 34 voltage and switching over time constants,

RF AGC response convergence when the electric field suddenly changes is improved.

Operation start time of the RF AGC can be delayed slightly by connecting a resistor parallel to the external capacitor

of pin 34.