ATR4258 datasheet(6/38 Pages) ATMEL

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ATR4258

4838A–AUDR–10/04

Test Mode

A special test mode is implemented for final production test only. This mode is activated

by setting bit 9 = 1. This mode is not intended to be used in customer applications.

For normal operation, bit 9 has to be set to 0. Bit 22 to bit 30 are deactivated in normal

operation mode.

VCO/Local Oscillator

Prescaler

An oscillator circuit is implemented to build a VCO as proposed in the application sche-

matic. The VCO frequency is used to generate the LO frequency of the 1

st mixer stages.

The control voltage of the VCO is usually generated by the PLL circuit U4256BM. The

VCO frequency has a range of 70 MHZ to 250 MHz to allow the reception of all analog

world bands.

A main element of the implemented oscillator circuit is a bipolar NPN transistor. The

internally biased base is connected to pin 13 and the emitter to pin 14. An AGC circuit

(bit 30) can be activated to increase the emitter current until the appropriate oscillation

level is reached. The fundamental emitter current can be changed by bit 52.

In addition (to the AM prescaler) a special VCO prescaler is implemented for all modes

(AM, WB and FM). The divider factor of the prescaler buffer provides the signal of the

buffered output (at pin 16) and the prescaler VCO provides the signal of the 1

st FM mixer

stage and AM prescaler. Examples of VCO prescaler settings are described in section

“Application Information” on page 29.

The divider factor of the VCO and buffer prescaler can be selected according Table 5 on

page 7.

Table 1. Operating Mode

AM/FM/Weather Channel

Bit 93

Bit 92

Bit 63

Bit 62

Standby

010

101

Weather band

Table 2. Test Mode

Mode

Bit 9

Normal operation

Test mode

Table 3. Local Oscillator AGC

Local Oscillator (VCO)

Bit 30

AGC off (default)

AGC on

Table 4. Local Oscillator Gain

Local Oscillator (VCO)

Bit 52

Low Gain

High Gain

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