2.9.6 VCO Tuning

The voltage-controlled oscillator (VCO) tuning process adjusts the digital frequency setting of the VCO before it is used in the analog PLL loop (see VCO). If the VCO is not tuned, the analog control voltage may be outside the operating range of the charge pump and the fractional-N-PLL does not lock. For this reason, the ATA8510/15 does not work reliably without VCO tuning.

During operation, a VCO tuning must be executed if the temperature changes by more than 40K or if the VCO frequency changes by more than 25 MHz. This change in VCO frequency corresponds to the following changes in the RF frequency:

  • Low-Band 310 MHz to 318 MHz: 3 MHz change
  • Low-Band 418 MHz to 477 MHz: 6 MHz change
  • High-Band 836 MHz to 956 MHz: 12 MHz change

It is generally recommended to activate VCO tuning during every receive or transmit service start-up.

As long as no VCO tuning process was performed after power-on, an initialization value is used from the EEPROM. The value can be configured independently for each service in the eepServices.FEVCT.FEVCT[3:0] variables. The default value is 7.

Address Service0

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

0x00D0

FEVCT

————

FEVCT[3:0]

A VCO tuning process can be triggered at the following time points:

  • During the start-up of a receive or transmit mode as the operating mode after the system start if enabled in eepTrxConf.sysStartConfig.VCO_TUNE.
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
0x0019 sysStartConfig RF_CAL ANT_TUNE VCO_TUNE IDLEModeSelector — TMDEN OPM[1:0]
  • During start-up of a receive or transmit mode via the “Set System Mode” SPI command (see Set System Mode).
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
systemModeConfig RF_CAL ANT_TUNE VCO_TUNE IDLEModeSelector — TMDEN OPM[1:0]
  • In PollingMode for each service/channel configuration (see VCO Tuning for additional information).

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

pollLoopConf[x].config

RfCalib

—

VCOtune

———

EOL

EOP

  • From IDLEMode via the “Calibrate and Check” SPI command if the EN_VCOCAL bit in tuneCheckConfig is set to ‘1’ (see Calibrate and Check).
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
tuneCheckConfig EN_ANT_TUNE EN_TEMP_MEAS EN_SRCCAL EN_FRCCAL EN_VCOCAL —EN_SELFCHECK —

Setting the VCO_CAL bit within the eepEventConf.cmdRdyConf command-ready variable to ‘1’ raises a command-ready (CMD_RDY) event on the event pin PB6 after the VCO tuning process finishes.

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

0x0096

cmdRdyConf

ANT_TUNE

TEMP_MEAS

SRC_CAL

FRC_CAL

VCO_CAL

RF_CAL

SELFCHECK

TX

VCO tuning requires additional time, see Timing Characteristics.