Rainbow Electronics ATA5746 User Manual

Features

• Transparent RF Receiver ICs for 315 MHz (ATA5746) and 433.92 MHz (ATA5745) With

High Receiving Sensitivity

• Fully Integrated PLL With Low Phase Noise VCO, PLL, and Loop Filter

• High FSK/ASK Sensitivity:–105 dBm (ATA5746, FSK, 9.6 Kbits/s, Manchester, BER 10

–114 dBm (ATA5746, ASK, 2.4 Kbits/s, Manchester, BER 10-3) –104 dBm (ATA5745, FSK, 9.6 Kbits/s, Manchester, BER 10 –113 dBm (ATA5745, ASK, 2.4 Kbits/s, Manchester, BER 10

• Supply Current: 6.5 mA in Active Mode (3V, 25°C, ASK Mode)

• Data Rate: 1 Kbit/s to 10 Kbits/s Manchester ASK, 1 Kbit/s to 20 Kbits/s Manchester

FSK With Four Programmable Bit Rate Ranges

• Switching Between Modulation Types ASK/FSK and Different Data Rates Possible in

≤1 ms Typically, Without Hardware Modification on Board to Allow Different Modulation Schemes for RKE, TPMS

• Low Standby Current: 50 µA at 3V, 25°C

• ASK/FSK Receiver Uses a Low-IF Architecture With High Selectivity, Blocking, and

Low Intermodulation (Typical 3-dB Blocking 68.0 dBC at ±3 MHz/74.0 dBC at ±20.0 MHz, System I1dBCP = –31dBm/System IIP3 = –24dBm)

• Telegram Pause Up to 52 ms Supported in ASK Mode

• Wide Bandwidth AGC to Handle Large Out-of-band Blockers above the System I1dBCP

• 440-kHz IF Frequency With 30-dB Image Rejection and 420-kHz IF Bandwidth to

Support PLL Transmitters With Standard Crystals or SAW-based Transmitters

• RSSI (Received Signal Strength Indicator) With Output Signal Dynamic Range of 65 dB

• Low In-band Sensitivity Change of Typically ±2.0 dB Within ±160-kHz Center

Frequency Change in the Complete Temperature and Supply Voltage Range

• Sophisticated Threshold Control and Quasi-peak Detector Circuit in the Data Slicer

• Fast and Stable XTO Start-up Circuit (> –1.4 kΩ Worst-case Start Impedance)

• Clock Generation for Microcontroller

• ESD Protection at all Pins (±4 kV HBM, ±200V MM, ±500V FCDM)

• Dual Supply Voltage Range: 2.7V to 3.3V or 4.5V to 5.5V

• Temperature Range: –40°C to +105°C

• Small 5 mm × 5 mm QFN24 Package

-3

)

) )

UHF ASK/FSK Receiver

ATA5745 ATA5746

Preliminary

Applications

• Automotive Keyless Entry and Tire Pressure Monitoring Systems

• Alarm, Telemetering and Energy Metering Systems

Benefits

• Supports Header and Blanking Periods of Protocols Common in RKE and TPM

Systems (Up to 52 ms in ASK Mode)

• All RF Relevant Functions are Integrated. The Single-ended RF Input is Suited for Easy

Adaptation to λ / 4 or Printed-loop Antennas

• Allows a Low-cost Application With Only 8 Passive Components

• Suitable for use in a Receiver for Joint RKE and TPMS

• Optimal Bandwidth Maximizes Sensitivity while Maintaining SAW Transmitter

Compatibility

• Clock Output Provides an External Microcontroller Crystal-precision Time Reference

• Well Suited for Use With PLL Transmitter ATA5756/ATA5757

4596A–RKE–05/06

1. General Description

The ATA5745/ATA5746 is a UHF ASK/FSK transparent receiver IC with low power consumption supplied in a small QFN24 package (body 5 mm × 5 mm, pitch 0.65 mm). ATA5745 is used in the 433 MHz to 435 MHz band of operation, and ATA5746 in 313 MHz to 317 MHz. The IC combines the functionality of remote keyless entry (RKE - typically low bit rate ASK) and tire pressure monitoring (TPM - typically high bit rate FSK) into one receiver under the control of an external microcontroller such as an ATmega48 (AVR

For improved image rejection and selectivity, the IF frequency is fixed to 440 kHz. The IF block uses an 8th-order band pass yielding a receive bandwidth of 420 kHz. This enables the use of the receiver in both SAW- and PLL-based transmitter systems utilizing various types of data-bit encoding such as pulse width modulation, Manchester modulation, variable pulse modulation, pulse position modulation, and NRZ. Prevailing encryption protocols such as Keeloq supported due to the receiver’s ability to hold the current data slicer threshold for up to 52 ms when incoming RF telegrams contain a blanking interval. This feature eliminates erroneous noise from appearing on the demodulated data output pin, and simplifies software decoding algorithms. The decoding of the data stream must be carried out by a connected microcontroller device. Because of the highly integrated design, the only required RF components are for the purpose of receiver antenna matching.

ATA5745 and ATA5746 support Manchester bit rates of 1 Kbit/s to 10 Kbits/s in ASK and 1 Kbit/s to 20 Kbits/s in FSK mode. The four discrete bit rate passbands are selectable and cover

1.0 Kbit/s to 2.5 Kbits/s, 2.0 Kbits/s to 5.0 Kbits/s, 4.0 Kbits/s to 10.0 Kbits/s, and 8.0 Kbits/s to

10.0 Kbits/s or 20.0 Kbits/s (for ASK or FSK, respectively). The receiver contains an RSSI output to provide an indication of received signal strength and a SENSE input to allow the customer to select a threshold below which the DATA signal is gated off. ASK/FSK and bit rate ranges are selected by the connected microcontroller device via pins ASK_NFSK, BR0, and BR1.

are easily

Figure 1-1. System Block Diagram

Antenna

RF Receiver

(LNA, Mixer,

Demodulator)

VCO, PLL,

IF Filter,

RSSI Amp.,

ATA5745/ATA5746

Digital Control

Logic

XTO

Powe r

Supply

Microcontroller

4 ... 8

Microcontroller

Interface

ATA5745/ATA5746 [Preliminary]

4596A–RKE–05/06

Figure 1-2. Pinning QFN24

ATA5745/ATA5746 [Preliminary]

TEST2 TEST1

CLK_OUT CLK_OUT_CTRL1 CLK_OUT_CTRL0

ENABLE

DATA_OUT

789101112

XTAL2

CDEM

23 22

XTAL1

BR1RXBR0

ASK_NFSK

21 20 19

VS5V

DVCC

S3V_AVCC

TEST3

RSSI

SENSE_CTRL

SENSE

LNA_IN LNA_GND

GND

Table 1-1. Pin Description

Pin Symbol Function

1 TEST2 Test pin, during operation at GND

2 TEST1 Test pin, during operation at GND

3 CLK_OUT Output to clock a connected microcontroller

4 CLK_OUT_CTRL1 Input to control CLK_OUT (MSB)

5 CLK_OUT_CTRL0 Input to control CLK_OUT (LSB)

6 ENABLE Input to enable the XTO

7 XTAL2 Reference crystal

8 XTAL1 Reference crystal

9 DVCC Digital voltage supply blocking

10 VS5V Power supply input for voltage range 4.5V to 5.5V

11 VS3V_AVCC Power supply input for voltage range 2.7V to 3.3V

12 GND Ground

13 LNA_GND RF ground

14 LNA_IN RF input

15 SENSE Sensitivity control resistor

16 SENSE_CTRL

17 RSSI Output of the RSSI amplifier

18 TEST3 Test pin, during operation at GND

19 RX Input to activate the receiver

20 BR0 Bit rate selection, LSB

21 BR1 Bit rate selection, MSB

22 ASK_NFSK

23 CDEM Capacitor to adjust the lower cut-off frequency data filter

24 DATA_OUT Data output

GND Ground/backplane (exposed die pad)

Sensitivity selection Low: Normal sensitivity, High: Reduced sensitivity

FSK/ASK selection Low: FSK, High: ASK

4596A–RKE–05/06

Figure 1-3. Block Diagram

CDEM

SENSE

SENSE_CTRL

GND

DVCC

LNA_IN

LNA_GND

ASK/FSK

Demo-

dulator

IF Amp

IF Filter

LPF

IF Amp

LPF

LNA VCO

ASK

FSK

PLL

(/24, /32)

Power

Supply

ASK/FSK

Control

Data Slicer

Standby

Logic Control

XTO

Div. by 3, 6, 12

XTO

VS3V_AVCC VS5V

ASK_NFSK

DATA_OUT BR0 BR1

CLK_OUT_CTRL1 CLK_OUT_CTRL0 CLK_OUT

RSSI

ENABLE

TEST1

TEST2

TEST3

XTAL2 XTAL1

ATA5745/ATA5746 [Preliminary]

4596A–RKE–05/06

2. RF Receiver

As seen in Figure 1-3 on page 4, the RF receiver consists of a low-noise amplifier (LNA), a local oscillator, and the signal processing part with mixer, IF filter, IF amplifier with analog RSSI, FSK/ASK demodulator, data filter, and data slicer.

In receive mode, the LNA pre-amplifies the received signal which is converted down to a 440-kHz intermediate frequency (IF), then filtered and amplified before it is fed into an FSK/ASK demodulator, data filter, and data slicer. The received signal strength indicator (RSSI) signal is available at the pin RSSI.

2.1 Low-IF Receiver

The receive path consists of a fully integrated low-IF receiver. It fulfills the sensitivity, blocking, selectivity, supply voltage, and supply current specification needed to design an automotive integrated receiver for RKE and TPM systems. A benefit of the integrated receive filter is that no external components needed.

At 315 MHz, the ATA5745 receiver (433.92 MHz for the ATA5746 receiver) has a typical system noise figure of 6.0 dB (7.0 dB), a system I1dBCP of –31 dBm (–30 dBm), and a system IIP3 of –24 dBm (–23 dBm). The signal path is linear for out-of-band disturbers up to the I1dBCP and hence there is no AGC or switching of the LNA needed, and a better blocking performance is achieved. This receiver uses an IF (intermediate frequency) of 440 kHz, the typical image rejection is 30 dB and the typical 3-dB IF filter bandwidth is 420 kHz (f f 10 Kbits/s Manchester with ±38 kHz frequency deviation in FSK mode, thus, the resulting sensitivity at 315 MHz (433.92 MHz) is typically –105 dBm (–104 dBm).

= 230 kHz and f

lo_IF

ATA5745/ATA5746 [Preliminary]

= 440 kHz ± 210 kHz,

= 650 kHz). The demodulator needs a signal-to-noise ratio of 8.5 dB for

hi_IF

Due to the low phase noise and spurs of the synthesizer together with the 8th-order integrated IF filter, the receiver has a better selectivity and blocking performance than more complex double superhet receivers, without using external components and without numerous spurious receiving frequencies.

A low-IF architecture is also less sensitive to second-order intermodulation (IIP2) than direct conversion receivers where every pulse or amplitude modulated signal (especially the signals from TDMA systems like GSM) demodulates to the receiving signal band at second-order non-linearities.

4596A–RKE–05/06

2.2 Input Matching at LNA_IN

The measured input impedances as well as the values of a parallel equivalent circuit of these impedances can be seen in Table 2-1. The highest sensitivity is achieved with power matching of these impedances to the source impedance.

Table 2-1. Measured Input Impedances of the LNA_IN Pin

fRF [MHz] ZIn(RF_IN) [Ω]R

433.92 (55 – j216) 900Ω//1.60

The matching of the LNA input to 50Ω is done using the circuit shown in Figure 2-1 and the val- ues of the matching elements given in Table 2-2. The reflection coefficients were always ≤ –10 dB. Note that value changes of C1 and L1 may be necessary to compensate individual board layout parasitics. The measured typical FSK and ASK Manchester-code sensitivities with a bit error rate (BER) of 10 ments were done with wire-wound inductors having quality factors reported in Table 2-2, resulting in estimated matching losses of 0.8 dB at 315 MHz and 433.92 MHz. These losses can be estimated when calculating the parallel equivalent resistance of the inductor with R

=2×π×f × L × QL and the matching loss with 10 log(1+R

loss

Figure 2-1. Input Matching to 50Ω

//C

In_p

[pF]

In_p

315 (72.4 – j298) 1300Ω//1.60

–3

are shown in Table 2-3 and Table 2-4 on page 7. These measure-

In_p/Rloss

Table 2-2. Input Matching to 50Ω

fRF [MHz] C1 [pF] L1 [nH] Q

315 2.2 68 20

433.92 2.2 36 15

ATA5745/ATA5746

LNA_IN

ATA5745/ATA5746 [Preliminary]

4596A–RKE–05/06

ATA5745/ATA5746 [Preliminary]

Table 2-3. Measured Typical Sensitivity FSK, ±38 kHz, Manchester, BER = 10

BR_Range_0

RF Frequency

315 MHz –108 dBm –108 dBm –107 dBm –105 dBm –104 dBm –104 dBm

433.92 MHz –107 dBm –107 dBm –106 dBm –104 dBm –103 dBm –103 dBm

1.0 Kbit/s

BR_Range_0

2.5 Kbits/s

BR_Range_1

5 Kbits/s

BR_Range_2

10 Kbits/s

Table 2-4. Measured Typical Sensitivity 100% ASK, Manchester, BER = 10

BR_Range_0

RF Frequency

315 MHz –114 dBm –114 dBm –113 dBm –111 dBm –109 dBm

433.92 MHz –113 dBm –113 dBm –112 dBm –110 dBm –108 dBm

1.0 Kbit/s

BR_Range_0

2.5 Kbits/s

BR_Range_1

5 Kbits/s

BR_Range_2

10 Kbits/s

–3

BR_Range_3

10 Kbits/s

–3

BR_Range_3

10 Kbits/s

BR_Range_3

20 Kbits/s

Conditions for the sensitivity measurement:

The given sensitivity values are valid for Manchester-modulated signals. For the sensitivity measurement the distance from edge to edge must be evaluated. As can be seen in Figure 6-1 on

page 24, in a Manchester-modulated data stream, the time segments T

To reach the specified sensitivity for the evaluation of T following limits should be used (T

min, TEE max, 2 × TEE min, 2 × TEE max).

and 2 × TEE in the data stream, the

and 2 × TEE occur.

Table 2-5. Limits for Sensitivity Measurements

Bit Rate TEE Min TEE Typ TEE Max 2 × TEE Min 2 × TEE Typ 2 × TEE Max

1.0 Kbit/s 260 µs 500 µs 790 µs 800 µs 1000 µs 1340 µs

2.4 Kbits/s 110 µs 208 µs 310 µs 320 µs 416 µs 525 µs

5.0 Kbits/s 55 µs 100 µs 155 µs 160 µs 200 µs 260 µs

9.6 Kbits/s 27 µs 52 µs 78 µs 81 µs 104 µs 131 µs

2.3 Sensitivity Versus Supply Voltage, Temperature and Frequency Offset

To calculate the behavior of a transmission system, it is important to know the reduction of the sensitivity due to several influences. The most important are frequency offset due to crystal oscillator (XTO) and crystal frequency (XTAL) errors, temperature and supply voltage dependency of the noise figure, and IF-filter bandwidth of the receiver. Figure 2-2 and Figure 2-3 on

page 8 show the typical sensitivity at 315 MHz, ASK, 2.4 Kbits/s and 9.6 Kbits/s, Manchester, Figure 2-4 and Figure 2-5 on page 9 show a typical sensitivity at 315 MHz, FSK, 2.4 Kbits/s and

9.6 Kbits/s, ±38 kHz, Manchester versus the frequency offset between transmitter and receiver at T

3.0V and 3.3V.

= –40°C, +25°C, and +105°C and supply voltage VS = VS3V_AVCC = VS5V = 2.7V,

amb

4596A–RKE–05/06

Figure 2-2. Measured Sensitivity (315 MHz, ASK, 2.4 Kbits/s, Manchester) Versus Fre-

(

quency Offset

Input Sensitivity (dBm) at BER < 1e-3, ATA5746, ASK, 2.4 Kbits/s (Manchester),

BR = 0

-118.00

-117.00

-116.00

-115.00

-114.00

-113.00

-112.00

-111.00

-110.00

-109.00

-108.00

-107.00

Input Sensitivity (dBm)

-106.00

-105.00

-104.00

-103.00

-300 -200 -100 0 100 200 300

delta RF (k Hz) at 315 MHz

2.7V / -40˚C

3.0V / -40˚C

3.3V / -40˚C

2.7V / 27˚C

3.0V / 27˚C

3.3V / 27˚C

2.7V / 105˚C

3.0V / 105˚C

3.3V / 105˚C

Figure 2-3. Measured Sensitivity (315 MHz, ASK, 9.6 Kbits/s, Manchester) Versus Fre-

quency Offset

Input Sensitivity (dBm) at BER < 1e-3, ATA5746, ASK, 9.6 Kbits/s (Manchester),

BR = 2

-115.00

-114.00

-113.00

-112.00

-111.00

-110.00

-109.00

-108.00

-107.00

-106.00

-105.00

Input Sensitivity (dBm)

-104.00

-103.00

-102.00

-101.00

-100.00

-300 -200 -100 0 100 200 300

2.7V / -40˚C

3.0V / -40˚C

3.3V / -40˚C

2.7V / 27˚C

3.0V / 27˚C

3.3V / 27˚C

2.7V / 105˚C

3.0V / 105˚C

3.3V / 105˚C

delta RF

ATA5745/ATA5746 [Preliminary]

kHz) at 315 MHz

4596A–RKE–05/06

ATA5745/ATA5746 [Preliminary]

Figure 2-4. Measured Sensitivity (315 MHz, FSK, 2.4 Kbits/s, ±38 kHz, Manchester) Versus

Frequency Offset

Input Sensitivity (dBm) at BER < 1e-3, ATA5746, FSK, 2.4 Kbits/s

(Manchester), BR0

-112.00

-111.00

-110.00

-109.00

-108.00

-107.00

-106.00

-105.00

-104.00

-103.00

-102.00

Input Sensitivity (dBm)

-101.00

-100.00

-99.00

-98.00

-300 -200 -100 0 100 200 300

2.7V / -40˚C

3.0V / -40˚C

3.3V / -40˚C

2.7V / 27˚C

3.0V / 27˚C

3.3V / 27˚C

2.7V / 105˚C

3.0V / 105˚C

3.3V / 105˚C

delta RF (k Hz) at 315 MHz

Figure 2-5. Measured Sensitivity (315 MHz, FSK, 9.6 Kbits/s, ±38 kHz, Manchester) Versus

Frequency Offset

Input Sensitivity (dBm) at BER < 1e-3, ATA5746, FSK, 9.6 Kbits/s (Manchester),

BR = 2

-110.00

-109.00

-108.00

-107.00

-106.00

-105.00

-104.00

-103.00

-102.00

-101.00

-100.00

-99.00

Input Sensitivity (dBm)

-98.00

-97.00

-96.00

-95.00

-300 -200 -100 0 100 200 300

2.7V / -40˚C

3.0V / -40˚C

3.3V / -40˚C

2.7V / 27˚C

3.0V / 27˚C

3.3V / 27˚C

2.7V / 105˚

3.0V / 105˚

3.3V / 105˚

4596A–RKE–05/06

delta RF (k Hz) at 315 MHz

As can be seen in Figure 2-5 on page 9, the supply voltage has almost no influence. The temperature has an influence of about ±1.0 dB, and a frequency offset of ±160 kHz also influences by about ±1 dB. All these influences, combined with the sensitivity of a typical IC (–105 dB), are then within a range of –103.0 dBm and –107.0 dBm over temperature, supply voltage, and frequency offset. The integrated IF filter has an additional production tolerance of ±10 kHz, hence, a frequency offset between the receiver and the transmitter of ±160 kHz can be accepted for XTAL and XTO tolerances.

Note: For the demodulator used in the ATA5745/ATA5746, the tolerable frequency offset does not

change with the data frequency. Hence, the value of ±160 kHz is valid for 1 Kbit/s to 10 Kbits/s.

This small sensitivity change over supply voltage, frequency offset, and temperature is very unusual in such a receiver. It is achieved by an internal, very fast, and automatic frequency correction in the FSK demodulator after the IF filter, which leads to a higher system margin. This frequency correction tracks the input frequency very quickly. If, however, the input frequency makes a larger step (for example, if the system changes between different communication partners), the receiver has to be restarted. This can be done by switching back to Standby mode and then again to Active mode (pin RX 1 ASK_NFSK (0

→1 → 0).

→ 0 → 1) or by generating a positive pulse on pin

2.4 Frequency Accuracy of the Crystals in a Combined RKE and TPM System

In a tire pressure measurement system working at 315 MHz and using an ATA5756 as transmitter and an ATA5746 is receiver, the higher frequency tolerances and the tolerance of the frequency deviation of the transmitter has to be considered.

In the TPM transmitter, the crystal has a frequency error over temperature –40°C to 125°C, aging, and tolerance of ±80 ppm (±25.2 kHz at 315 MHz). The tolerances of the XTO, the capacitors used for FSK modulation, and the stray capacitances cause an additional frequency error of ±30 ppm (±9.45 kHz at 315 MHz). The frequency deviation of such a transmitter varies between ±16 kHz and ±24 kHz, since a higher frequency deviation is equivalent to a frequency error this has to be considered as an additional ±24 kHz – ±19.5 kHz = ±4.5kHz frequency tolerance (19.5 kHz is constant). All tolerances added, these transmitters have a worst-case frequency offset of ±39.15 kHz.

For the receiver in the car, a tolerance of ±160 kHz – ±39.15 kHz = ±120.85 kHz (±383.6 ppm) remains. The needed frequency stability of the crystals over temperature and aging is ±383.6 ppm – ±5 ppm = ±378.6 ppm. The aging of such a crystal is ±10 ppm, leaving a reasonable ±368.6 ppm for the temperature dependency of the crystal frequency in the car.

Since the receiver in the car is able to receive these TPM transmitter signals with high frequency offsets, the component specification in the key can be largely relaxed.

This system calculation is based on worst-case tolerances of all the components; this leads in practice to a system with margin.

For a 433.92 MHz TPM system using ATA5757 as transmitter and ATA5745 as receiver, the same calculation must be done, but since the RF frequency is higher, every ppm of crystal tolerances results in higher frequency offset and either the system must have lower tolerances or a lower margin at this frequency.

ATA5745/ATA5746 [Preliminary]

4596A–RKE–05/06

ATA5745/ATA5746 [Preliminary]

)

2.5 RX Supply Current Versus Temperature and Supply Voltage

Table 2-7 shows the typical supply current of the receiver in Active mode versus supply voltage

and temperature with VS = VS3V_AVCC = VS5V.

Table 2-6. Measured Current in Active Mode ASK

VS = VS3V_AVCC = VS5V 2.7V 3.0V 3.3V

= –40°C 5.4 mA 5.5 mA 5.6 mA

amb

= 25°C 6.4 mA 6.5 mA 6.6 mA

amb

= 105°C 7.4 mA 7.5 mA 7.6 mA

amb

Table 2-7. Measured Current in Active Mode FSK

VS = VS3V_AVCC = VS5V 2.7V 3.0V 3.3V

= –40°C 5.6 mA 5.7 mA 5.8 mA

amb

= 25°C 6.6 mA 6.7 mA 6.8 mA

amb

= 105°C 7.6 mA 7.7 mA 7.8 mA

amb

2.6 Blocking, Selectivity

As can be seen in Figure 2-6 on page 11, and Figure 2-7 and Figure 2-8 on page 12, the receiver can receive signals 3 dB higher than the sensitivity level in the presence of large blockers of –34.5 dBm or –28 dBm with small frequency offsets of ±3 MHz or ±20 MHz.

Figure 2-6, and Figure 2-7 on page 12 show the narrow-band blocking, and Figure 2-8 on page 12 shows the wide-band blocking characteristic. The measurements were done with a useful

signal of 315 MHz, FSK, 10 Kbits/s, ±38 kHz, Manchester, BR_Range2 with a level of –105 dBm + 3 dB = –102 dBm, which is 3 dB above the sensitivity level. The figures show how much larger than –102 dBm a continuous wave signal can be, until the BER is higher than 10

–3

The measurements were done at the 50Ω input shown in Figure 2-1 on page 6. At 3 MHz, for example, the blocker can be 67.5 dBC higher than –102 dBm, or –102 dBm + 67.5 dBC = –34.5 dBm.

Figure 2-6. Close-in 3-dB Blocking Characteristic and Image Response at 315 MHz

70 .0

60.0

50 .0

40.0

30.0

20.0

10 .0

Blocking Level (dBC)

0.0

-10.0

-2 .0 -1.5 -1.0 -0 .5 0.0 0.5 1.0 1.5 2.

Distance from Interfering to Receiving Signal (MHz

4596A–RKE–05/06

Figure 2-7. Narrow-band 3-dB Blocking Characteristic at 315 MHz

80.0

70 .0

60.0

50 .0

40.0

30.0

20.0

10 .0

Blocking Level (dBC)

0.0

-10.0

-5.0 -4 .0 -3 .0 - 2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.

Distance from Interfering to Receiving Signal (MHz)

Figure 2-8. Wide-band 3-dB Blocking Characteristic at 315 MHz

80.0

70 .0

60.0

50 .0

40.0

30.0

20.0

10 .0

Blocking Level (dBC)

0.0

-10.0

-50.0 -40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.

Distance from Interfering to Receiving Signal (MHz)

Table 2-8 shows the blocking performance measured relative to –102 dBm for some frequen-

cies. Note that sometimes the blocking is measured relative to the sensitivity level 104 dBm (denoted dBS), instead of the carrier –102 dBm (denoted dBC)

Table 2-8. Blocking 3 dB Above Sensitivity Level With BER < 10

Frequency Offset Blocking Level Blocking

+1.5 MHz –44.5 dBm 57.5 dBC, 60.5 dBS

–1.5 MHz –44.5 dBm 57.5 dBC, 60.5 dBS

+2 MHz –39.0 dBm 63 dBC, 66 dBS

–2 MHz –36.0 dBm 66 dBC, 69 dBS

+3 MHz –34.5 dBm 67.5 dBC, 70.5 dBS

–3 MHz –34.5 dBm 67.5 dBC, 70.5 dBS

+20 MHz –28.0 dBm 74 dBC, 77 dBS

–20 MHz –28.0 dBm 74 dBC, 77 dBS

ATA5745/ATA5746 [Preliminary]

–3

4596A–RKE–05/06

ATA5745/ATA5746 [Preliminary]

)

C C C

The ATA5745/ATA5746 can also receive FSK and ASK modulated signals if they are much higher than the I1dBCP. It can typically receive useful signals at to as the nonlinear dynamic range (that is, the maximum to minimum receiving signal), and is 95 dB for 10 Kbits/s Manchester (FSK). This value is useful if the transmitter and receiver are very close to each other.

2.7 In-band Disturbers, Data Filter, Quasi-peak Detector, Data Slicer

If a disturbing signal falls into the received band, or if a blocker is not a continuous wave, the performance of a receiver strongly depends on the circuits after the IF filter. Hence, the demodulator, data filter, and data slicer are important.

The data filter of the ATA5745/ATA5746 functions also as a quasi-peak detector. This results in a good suppression of above mentioned disturbers and exhibits a good carrier-to-noise performance. The required useful-signal-to-disturbing-signal ratio, at a BER of 10 in ASK mode and less than 3 dB (BR_Range_0 to BR_Range_2) and 6 dB (BR_Range_3) in FSK mode. Due to the many different possible waveforms, these numbers are measured for the signal, as well as for disturbers, with peak amplitude values. Note that these values are worst-case values and are valid for any type of modulation and modulating frequency of the disturbing signal, as well as for the receiving signal. For many combinations, lower carrier-to-disturbing-signal ratios are needed.

–10 dBm. This is often referred

–3,

is less than 14 dB

2.8 RSSI Output

The output voltage of the pin RSSI is an analog voltage, proportional to the input power level. Using the RSSI output signal, the signal strength of different transmitters can be distinguished. The usable dynamic range of the RSSI amplifier is 65 dB, the input power range P(RF

) is –110 dBm to –45 dBm, and the gain is 15 mV/dB. Figure 2-9 shows the RSSI characteristic of a typical device at 315 MHz with VS3V_AVCC = VS5V = 2.7V to 3.3V and T

= –40°C to

amb

+105°C with a matched input as shown in Table 2-2 and Figure 2-1 on page 6. At 433.92 MHz, 1 dB more signal level is needed for the same RSSI results.

Figure 2-9. Typical RSSI Characteristic at 315 MHz Versus Temperature and Supply Voltage

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

V_RSSI (V)

0.9

0.8

0.7

0.6

0.5

0.4

-130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10

Pin (dBm

min; -9dB max; +9dB

2.7V, -40˚C

3.0V, -40˚C

3.3V, -40˚C

2.7V, 27˚C

3.0V, 27˚C

3.3V, 27˚C

2.7V, 105˚

3.0V, 105˚

3.3V, 105˚

4596A–RKE–05/06

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