SI4311-B12-GMR Просмотр технического описания (PDF) - Silicon Laboratories

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SI4311-B12-GMR

315/433.92 MHZ FSK RECEIVER

Silicon Laboratories 

Si4311-B12/B21

3.2. Receiver Description

The RF input signal is amplified by a low-noise amplifier

(LNA) and down-converts to a low intermediate

frequency with a quadrature image-reject mixer. The

mixer output is amplified by a programmable gain

amplifier (PGA), filtered, and digitized with a high-

resolution analog-to-digital converter (ADC). All RF

functions are integrated into the device eliminating any

production alignment issues associated with external

components, such as SAW and ceramic IF filters.

Silicon Labs’ advanced digital low-IF architecture

achieves superior performance by using the DSP to

perform channel filtering, demodulation, automatic gain

control (AGC), automatic frequency control (AFC), and

other baseband processing. DSP implementation of the

channel filters provides better repeatability and control

of the bandwidth and frequency response of the filter

compared to analog implementations. No off-chip

ceramic filters are needed with the Si4311 since all IF

channel filtering is performed in the digital domain.

by driving Pin 6 (315/434) to VDD or GND. The

315 MHz operation is chosen by driving Pin 6 (315/434)

to VDD, and 433.92 MHz operation is chosen by driving

Pin 6 (315/434) to GND.

Table 8. Carrier Frequency Selection

Pin 6 (315/434)

0

1

Frequency [MHz]

433.92

315

3.4. Bit Time BT[1:0] Selection

The Si4311 can operate with data rates of up to 10 kbps

non-return to zero (NRZ) data or 5 kbps Manchester

encoded data. However, FSK modulation uses other

encoding schemes, such as pulse width modulation

(PWM) and pulse position modulation (PPM) in which a

bit can be encoded into a pulse with a certain duty cycle

or pulse width (see Figure 4).

3.3. Carrier Frequency Selection

The Si4311 can be tuned to either 315 or 433.92 MHz

Digital Data

“1”

“0”

“1”

“1”

NRZ

Encoding

Manchester

Encoding

PPM

Encoding

1000 us

100 us

Figure 4. Example Data Waveforms

actual data rate is 1 kbps (1000 µs). After finding BT,

In order to set the data filter bandwidth correctly, the

shortest pulse width of the transmitted encoded data

should be chosen as the bit time. In the PPM example

shown in Figure 4, the shortest pulse width is 100 µs, so

Table 9 can be used to find the bit settings for pins 14

and 15, BT[1:0]. In this PPM example, BT[1:0] is set as

logic BT1 = 1 and BT0 = 1 or BT[1:0] = (1,1) since

BT = 100 µs.

the bit time is chosen as BT = 100 µs even though the

Table 9. How to Choose BT[1:0] Based on the Bit Time

Bit Time [us]

BT ≥ 1000

1000< BT ≤ 500

BT1 (pin 14)

0

0

BT0 (pin 15)

0

1

Rev. 1.0

9

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