13

µPC2533

2.3

MIX2 Block

Fig. 2-3 MIX2 Block

28

23

17

24

25

14

13

12

11

22

21

Note

Xtal

R211

R212

+

R210

R209

R207

R208

Q205

Q206

Q207

Q208

Q201

Q202

Q203

Q204

Q203

OSC2

Buff2

To IF amplifier

Bias

circuit

To RF AGC circuit (Fig. 2-4)

From IF AGC (Fig. 2-6)

Current control

circuit

Note

From 10.7 MHz BPF

Note Output impedance and input impedance of Buff2 are 2 k

Ω and 30 kΩ, respectively.

MIX2 (Q201 to Q208) is a DBM with a configuration similar to that of MIX1.

The major difference from the MIX1 is that MIX2 is equipped with a current control circuit for output and is controlled

by the AGC.

Input impedance of MIX2 is 330

Ω to match the 10.7 MHz ceramic filter. Output impedance of Buff2 is 2 kΩ to

match the 450 kHz ceramic filter.

IF signal input from pin 23 is also input to the detector of the RF AGC. The RF AGC is detected by both MIX1 and

MIX2 blocks.

The Buff1 and Buff2 ensure impedance matching between MIX1 and MIX2 outputs and each ceramic filter. As

a result, IFT design is not restricted by the need to match ceramic filter impedance. For turn ratio, etc., only conversion

gain need be taken input account, so it is easy to design.