4

4950B–GPS–11/06

ATR0603 [Preliminary]

3.6

IF Filter

The mixer directly drives an external LC bandpass filter via open collector outputs. In order to

provide highest selectivity and conversion gain, it is recommended to design the external filter,

according to the application proposal in chapter 10, as a 2-pole filter with a quality factor Q > 25.

3.7

IF Amplifier

The output of the IF filter drives an IF amplifier which is combined with additional low-pass filter-

ing. The gain of this amplifier can be set to three different levels in order to optimally charge the

input of the following analog-to-digital converter for each application.

The gain is internally set to high gain mode but can be adjusted by using external pull-down

resistors at pin 18 (AMP1) and pin 19 (AMP2). If high gain mode is desired, pins 18 and 19 have

to be left floating (see Section 8. ”Electrical Characteristics” ).

3.8

A/D Converter

The analog-to-digital converter stage has a total resolution of 1 bit. It comprises a sub-sampling

unit, clocked by the reference frequency (f

signal (f

selected sub-sampling factor (n = 6) leads to the designated digital output signal, with a center

frequency given by:

f

=

3.9

Clock and Data Driver

CMOS output drivers provide the output bit as well as the system clock to the baseband IC. The

amplitude of this signal strongly depends on the value for the digital supply voltage (see Section