9

ATA8203/ATA8204/ATA8205 [DATASHEET]

9121D–INDCO–09/14

5.

Receiving Characteristics

automotive application, a SAW filter is used to achieve better selectivity and large signal capability. The receiving frequency

response without a SAW front-end filter is illustrated in Figure 5-1 “Narrow Band Receiving Frequency Response ATA8204”.

This example relates to ASK mode. FSK mode exhibits a similar behavior. The plots are printed relatively to the maximum

sensitivity. If a SAW filter is used, an insertion loss of about 3dB must be considered, but the overall selectivity is much

better.

When designing the system in terms of receiving bandwidth, the LO deviation must be considered as it also determines the

IF center frequency. The total LO deviation is calculated, to be the sum of the deviation of the crystal and the XTO deviation

of the Atmel ATA8203/ATA8204/ATA8205. Low-cost crystals are specified to be within ±90ppm over tolerance, temperature,

and aging. The XTO deviation of the Atmel ATA8203/ATA8204/ATA8205 is an additional deviation due to the XTO circuit.

This deviation is specified to be ±10ppm worst case for a crystal with CM = 7fF. If a crystal of ±90ppm is used, the total

deviation is ±100ppm in that case. Note that the receiving bandwidth and the IF-filter bandwidth are equivalent in ASK mode

but not in FSK mode.

Figure 5-1. Narrow Band Receiving Frequency Response ATA8204

6.

Polling Circuit and Control Logic

The receiver is designed to consume less than 1 mA while being sensitive to signals from a corresponding transmitter. This

is achieved using the polling circuit. This circuit enables the signal path periodically for a short time. During this time the bit-

check logic verifies the presence of a valid transmitter signal. Only if a valid signal is detected, the receiver remains active

and transfers the data to the connected microcontroller. If there is no valid signal present, the receiver is in sleep mode most

of the time resulting in low current consumption. This condition is called polling mode. A connected microcontroller is

disabled during that time.

All relevant parameters of the polling logic can be configured by the connected microcontroller. This flexibility enables the

user to meet the specifications in terms of current consumption, system response time, data rate etc.

The receiver is very flexible with regards to the number of connection wires to the microcontroller. It can be either operated

by a single bi-directional line to save ports to the connected microcontroller or it can be operated by up to five uni-directional

ports.

(MHz)

430

431

432

433

434

435

436

437

438

4.5V -40°C

5.0V -40°C

5.5V -40°C

4.5V 25°C

5.0V 25°C

5.5V 25°C

-40

-30

-20

-70

-60

-50

-10

0

10

Image Rejection versus RF Frequency