Direct-Conversion Tuner ICs for

Digital DBS Applications

10

______________________________________________________________________________________

28

27

26

25

24

23

22

21

20

56

Ω

33

Ω

19

18

17

16

15

0.22

µF

0.22

µF

22pF

22pF

10pF

1000pF

22

Ω

10pF

2

1

3

4

5

6

7

8

9

10

11

12

13

14

IOUT

GND

RFIN

RFIN

GND

GND

AGC

CONTROL

100

Ω

LOAD

AGC

GND

GND

QOUT

PRESCALER

OUTPUT

LO

INPUT

(50

Ω

SOURCE)

MODULUS

CONTROL

MOD

PSOUT

LO

LO

GND

PSGND

GND

IDC

IDC

QDC

QDC

10pF

1000pF

22pF

22pF

22pF

22pF

51

Ω

0.1

µF

0.1

µF

10pF

47

µF

0.1

µF

47

µF

RF

INPUT

(50

Ω

SOURCE)

MAX2102

MAX2105

2k

Ω

100

Ω

LOAD

0.1

µF

Figure 1. Typical Operating Circuit

Detailed Description

The MAX2102/MAX2105 down-convert signals in the

range 950MHz to 2150MHz directly to baseband I/Q

signals. They are targeted for digital DBS tuner applica-

tions where a direct downconversion provides a cost

savings over prior-art, multiple-conversion approaches.

However, the MAX2102/MAX2105 are applicable to any

system requiring a broadband I/Q downconversion.

Internally, the MAX2102 and MAX2105 consist of a

broadband front-end variable gain stage, a quadrature

downconverter, an oscillator buffer, high-linearity I and

Q baseband amplifiers, and offset correction amplifiers.

The MAX2102 features a front-end AGC dynamic range

of over 50dB, while the MAX2105 provides a front-end

AGC dynamic range of over 41dB. Specifically, the

AGC control can be adjusted so that a sine wave at

RFIN ranging in power from -69dBm to -19dBm

(MAX2102) or -60dBm to -19dBm (MAX2105) will pro-

duce a sine wave at IOUT and QOUT at 500mVp-p lev-

els. The noise figure is lowest when the AGC is at its

maximum gain setting (see

Typical Operating

Characteristics). The VSWR at RFIN is unaffected by

the AGC setting.

The local-oscillator (LO) buffer accepts an external LO

signal at LO, LO, and internally limits the signal to pro-

vide a consistent on-chip LO level. The LO input drive

level should be maintained within the specified limits

(see

Applications Information section).