Direct-Conversion Tuner ICs for

Digital DBS Applications

______________________________________________________________________________________

11

BASEBAND LP FILTERS

(OPTIONAL

GAIN)

DSP:

QPSK

DEMOD

0.1

µF

0.1

µF

L1

L2

L3

OR

C1

C2

C3

C4

0

90

ADC

ADC

AGC

MAX1002

MAX1003

IDC

QDC

IDC

LO

AGC

IOUT

QOUT

DIV

RFIN

RFIN

EXTERNAL

VCO

LO

OFFSET CORRECTION

OR

QDC

PSOUT

TANK

TSA5055

OR EQUIV.

MOD

0.1

µF

0.1

µF

L1

L2

L3

C1

C2

C3

C4

KU BAND

75

Ω CABLE

950MHz to 2150MHz

F-CONNECTOR

INPUT

F-CONNECTOR

FOR 2nd SET-TOP BOX

LNB

MAX2102

MAX2105

Figure 2. Typical Application

The quadrature downconverter follows the front-end

AGC. Two mixers are driven by the previous stage

AGC amplifier output. The mixer LO ports are fed with

the two LO signals, which are 90° apart in phase.

These quadrature LO signals are generated on-chip

using the LO signal from the LO buffer.

The resulting I/Q baseband signals are fed through

separate I and Q channel baseband amplifiers. Robust

output stages drive IOUT and QOUT. The outputs are

capable of driving lowpass filters with 100

Ω character-

istic impedance (that is, the equivalent of an AC-cou-

pled, 100

Ω load). The baseband -3dB output band-

width is over 90MHz.

__________Applications Information

Front-End Tuner Circuitry

for DBS Tuners

In a typical application, the signal path ahead of the

MAX2102/MAX2105 will include a discrete LNA/buffer

and a PIN-diode attenuator. Alternatively, a dual-gate