SWRS045F January   2006  – November 2018 CC1021

PRODUCTION DATA.  

  1. 1Device Overview
    1. 1.1 Features
    2. 1.2 Applications
    3. 1.3 Description
    4. 1.4 Functional Block Diagram
  2. 2Revision History
  3. 3Terminal Configuration and Functions
    1. 3.1 Pin Diagram
    2. 3.2 Pin Configuration
  4. 4Specifications
    1. 4.1  Absolute Maximum Ratings
    2. 4.2  ESD Ratings
    3. 4.3  Recommended Operating Conditions
    4. 4.4  RF Transmit
    5. 4.5  RF Receive
    6. 4.6  RSSI / Carrier Sense
    7. 4.7  Intermediate Frequency (IF)
    8. 4.8  Crystal Oscillator
    9. 4.9  Frequency Synthesizer
    10. 4.10 Digital Inputs / Outputs
    11. 4.11 Current Consumption
    12. 4.12 Thermal Resistance Characteristics for VQFNP Package
  5. 5Detailed Description
    1. 5.1  Overview
    2. 5.2  Functional Block Diagram
    3. 5.3  Configuration Overview
      1. 5.3.1 Configuration Software
    4. 5.4  Microcontroller Interface
      1. 5.4.1 Configuration Interface
      2. 5.4.2 Signal Interface
      3. 5.4.3 PLL Lock Signal
    5. 5.5  4-wire Serial Configuration Interface
    6. 5.6  Signal Interface
      1. 5.6.1 Synchronous NRZ Mode
      2. 5.6.2 Transparent Asynchronous UART Mode
      3. 5.6.3 Synchronous Manchester Encoded Mode
        1. 5.6.3.1 Manchester Encoding and Decoding
    7. 5.7  Data Rate Programming
    8. 5.8  Frequency Programming
      1. 5.8.1 Dithering
    9. 5.9  Receiver
      1. 5.9.1  IF Frequency
      2. 5.9.2  Receiver Channel Filter Bandwidth
      3. 5.9.3  Demodulator, Bit Synchronizer and Data Decision
      4. 5.9.4  Receiver Sensitivity versus Data Rate and Frequency Separation
      5. 5.9.5  RSSI
      6. 5.9.6  Image Rejection Calibration
      7. 5.9.7  Blocking and Selectivity
      8. 5.9.8  Linear IF Chain and AGC Settings
      9. 5.9.9  AGC Settling
      10. 5.9.10 Preamble Length and Sync Word
      11. 5.9.11 Carrier Sense
      12. 5.9.12 Automatic Power-Up Sequencing
      13. 5.9.13 Automatic Frequency Control
      14. 5.9.14 Digital FM
    10. 5.10 Transmitter
      1. 5.10.1 FSK Modulation Formats
      2. 5.10.2 Output Power Programming
      3. 5.10.3 TX Data Latency
      4. 5.10.4 Reducing Spurious Emission and Modulation Bandwidth
    11. 5.11 Input and Output Matching and Filtering
    12. 5.12 Frequency Synthesizer
      1. 5.12.1 VCO, Charge Pump, and PLL Loop Filter
      2. 5.12.2 VCO and PLL Self-Calibration
      3. 5.12.3 PLL Turn-on Time versus Loop Filter Bandwidth
      4. 5.12.4 PLL Lock Time versus Loop Filter Bandwidth
    13. 5.13 VCO and LNA Current Control
    14. 5.14 Power Management
    15. 5.15 On-Off Keying (OOK)
    16. 5.16 Crystal Oscillator
    17. 5.17 Built-in Test Pattern Generator
    18. 5.18 Interrupt on Pin DCLK
      1. 5.18.1 Interrupt Upon PLL Lock
      2. 5.18.2 Interrupt Upon Received Signal Carrier Sense
    19. 5.19 PA_EN and LNA_EN Digital Output Pins
      1. 5.19.1 Interfacing an External LNA or PA
      2. 5.19.2 General-Purpose Output Control Pins
      3. 5.19.3 PA_EN and LNA_EN Pin Drive
    20. 5.20 System Considerations and Guidelines
      1. 5.20.1 SRD Regulations
      2. 5.20.2 Narrowband Systems
      3. 5.20.3 Low Cost Systems
      4. 5.20.4 Battery Operated Systems
      5. 5.20.5 High Reliability Systems
      6. 5.20.6 Frequency Hopping Spread Spectrum Systems (FHSS)
    21. 5.21 Antenna Considerations
    22. 5.22 Configuration Registers
      1. 5.22.1 Memory
  6. 6Applications, Implementation, and Layout
    1. 6.1 Application Information
      1. 6.1.1 Typical Application
    2. 6.2 Design Requirements
      1. 6.2.1 Input / Output Matching
      2. 6.2.2 Bias Resistor
      3. 6.2.3 PLL Loop Filter
      4. 6.2.4 Crystal
      5. 6.2.5 Additional Filtering
      6. 6.2.6 Power Supply Decoupling and Filtering
    3. 6.3 PCB Layout Guidelines
  7. 7Device and Documentation Support
    1. 7.1 Device Support
      1. 7.1.1 Device Nomenclature
    2. 7.2 Documentation Support
      1. 7.2.1 Community Resources
    3. 7.3 Trademarks
    4. 7.4 Electrostatic Discharge Caution
    5. 7.5 Export Control Notice
    6. 7.6 Glossary
  8. 8Mechanical Packaging and Orderable Information
    1. 8.1 Packaging Information

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订购信息

Linear IF Chain and AGC Settings

The CC1021 device is based on a linear IF chain where the signal amplification is done in an analog VGA (Variable Gain Amplifier). The gain is controlled by the digital part of the IF chain after the ADC (Analog to Digital Converter). The AGC (Automatic Gain Control) loop ensures that the ADC operates inside its dynamic range by using an analog/digital feedback loop.

The maximum VGA gain is programmed by the VGA_SETTING[4:0] in the VGA3 register. The VGA gain is programmed in approximately 3 dB/LSB. The VGA gain should be set so that the amplified thermal noise from the front-end balance the quantization noise from the ADC. Therefore the optimum maximum VGA gain setting will depend on the channel filter bandwidth.

A digital RSSI is used to measure the signal strength after the ADC. The CS_LEVEL[4:0] in the VGA4 register is used to set the nominal operating point of the gain control (and also the carrier sense level). Further explanation can be found in Figure 5-17.

The VGA gain will be changed according to a threshold set by the VGA_DOWN[2:0] in the VGA3 register and the VGA_UP[2:0] in the VGA4 register. Together, these two values specify the signal strength limits used by the AGC to adjust the VGA gain.

To avoid unnecessary tripping of the VGA, an extra hysteresis and filtering of the RSSI samples can be added. The AGC_HYSTERESIS bit in the VGA2 register enables this.

The time dynamics of the loop can be altered by the VGA_BLANKING bit in the ANALOG register, and VGA_FREEZE[1:0] and VGA_WAIT[2:0] bits in the VGA1 register.

When VGA_BLANKING is activated, the VGA recovery time from DC offset spikes after a gain step is reduced.

VGA_FREEZE determines the time to hold bit synchronization, VGA and RSSI levels after one of these events occur:

  • RX power-up
  • The PLL has been out of lock
  • Frequency register setting is switched between A and B

This feature is useful to avoid AGC operation during start-up transients and to ensure minimum dwell time using frequency hopping. This means that bit synchronization can be maintained from hop to hop.

VGA_WAIT determines the time to hold the present bit synchronization and RSSI levels after changing VGA gain. This feature is useful to avoid AGC operation during the settling of transients after a VGA gain change. Some transients are expected due to DC offsets in the VGA.

At the sensitivity limit, the VGA gain is set by VGA_SETTING. In order to optimize selectivity, this gain should not be set higher than necessary. The SmartRF™ Studio software gives the settings for VGA1 through VGA4 registers. For reference, the following method can be used to find the AGC settings:

  1. Disable AGC and use maximum LNA2 gain by writing BFh to the VGA2 register. Set minimum VGA gain by writing to the VGA3 register with VGA_SETTING = 0.
  2. Apply no RF input signal, and measure ADC noise floor by reading the RSSI register.
  3. Apply no RF input signal, and write VGA3 register with increasing VGA_SETTING value until the RSSI register value is approximately 4 larger than the value read in step 2. This places the front-end noise floor around 6 dB above the ADC noise floor.
  4. Apply an RF signal with strength equal the desired carrier sense threshold. The RF signal should preferably be modulated with correct Baud rate and deviation. Read the RSSI register value, subtract 8, and write to CS_LEVEL in the VGA4 register. Vary the RF signal level slightly and check that carrier sense indication (bit 3 in STATUS register) switches at the desired input level.
  5. If desired, adjust the VGA_UP and VGA_DOWN settings according to the explanation in Figure 5-17.
  6. Enable AGC and select LNA2 gain change level. Write 55h to VGA2 register if the resulting VGA_SETTING>10. Otherwise, write 45h to VGA2. Modify AGC_AVG in the above VGA2 value if faster carrier sense and AGC settling is desired.

CC1021 rltnshp_btwn_rssi_carrier_agc_vga_swrs045.gifFigure 5-17 Relationship Between RSSI, Carrier Sense Level,
and AGC Settings CS_LEVEL, VGA_UP and VGA_DOWN