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Original question:

CC1310: Very severe 10dbm loss over balun in CC1310 design

CC1310: Single-ended link to an antenna in cc1310 design

GregoireGentil
Expert 2330 points
Part Number: CC1310
Other Parts Discussed in Thread: CC1350STK

I'm trying to link a cc1310 to a very well-tuned antenna without using a balun. I directly link RFN to the antenna and leave floating RFP as well as TXRX.

My settings code is the following. I have frontendMode = 2 and biasMode = 0. The performance is very bad. Is there something else I should be aware of? The antenna is extremely good and I have both cc1310 and the same antenna running the same code on both sides. performance is OK but not outstanding. The Excel Range Estimator says that I should get 100s meters.

(Note that the antenna has a direct connection to ground so I have also tested with a 100pF capacitor between RFN and the antenna).

Also, is it better not to use the internal bias? Then how to calculated the inductor value?

//*********************************************************************************
// Generated by SmartRF Studio version 2.13.0 (build#170)
// The applied template is compatible with CC13x0 SDK version 2.10.xx.xx or newer.
// Device: CC1310 Rev. B (2.1)
//
//*********************************************************************************


//*********************************************************************************
// Parameter summary
// RX Address0: 0xAA 
// RX Address1: 0xBB 
// RX Address Mode: No address check 
// Frequency: 915.00000 MHz
// Data Format: Serial mode disable 
// Deviation: 175.000 kHz
// Packet Length Config: Variable 
// Max Packet Length: 255 
// Packet Length: 20 
// Packet Data: 255 
// RX Filter BW: 1243 kHz
// Symbol Rate: 500.00000 kBaud
// Sync Word Length: 32 Bits 
// TX Power: 14 dBm (requires define CCFG_FORCE_VDDR_HH = 1 in ccfg.c, see CC13xx/CC26xx Technical Reference Manual)
// Whitening: No whitening 

#include <ti/devices/DeviceFamily.h>
#include DeviceFamily_constructPath(driverlib/rf_mailbox.h)
#include DeviceFamily_constructPath(driverlib/rf_common_cmd.h)
#include DeviceFamily_constructPath(driverlib/rf_prop_cmd.h)
#include <ti/drivers/rf/RF.h>
#include DeviceFamily_constructPath(rf_patches/rf_patch_cpe_genfsk.h)
#include DeviceFamily_constructPath(rf_patches/rf_patch_rfe_genfsk.h)
#include "smartrf_settings.h"


// TI-RTOS RF Mode Object
RF_Mode RF_prop =
{
    .rfMode = RF_MODE_PROPRIETARY_SUB_1,
    .cpePatchFxn = &rf_patch_cpe_genfsk,
    .mcePatchFxn = 0,
    .rfePatchFxn = &rf_patch_rfe_genfsk
};


// Overrides for CMD_PROP_RADIO_DIV_SETUP
uint32_t pOverrides[] =
{
    // override_use_patch_prop_genfsk.xml
    // PHY: Use MCE ROM bank 4, RFE RAM patch
    MCE_RFE_OVERRIDE(0,4,0,1,0,0),
    // override_synth_prop_863_930_div5.xml
    // Synth: Set recommended RTRIM to 7
    HW_REG_OVERRIDE(0x4038,0x0037),
    // Synth: Set Fref to 4 MHz
    (uint32_t)0x000684A3,
    // Synth: Configure fine calibration setting
    HW_REG_OVERRIDE(0x4020,0x7F00),
    // Synth: Configure fine calibration setting
    HW_REG_OVERRIDE(0x4064,0x0040),
    // Synth: Configure fine calibration setting
    (uint32_t)0xB1070503,
    // Synth: Configure fine calibration setting
    (uint32_t)0x05330523,
    // Synth: Set loop bandwidth after lock to 20 kHz
    (uint32_t)0x0A480583,
    // Synth: Set loop bandwidth after lock to 20 kHz
    (uint32_t)0x7AB80603,
    // Synth: Configure VCO LDO (in ADI1, set VCOLDOCFG=0x9F to use voltage input reference)
    ADI_REG_OVERRIDE(1,4,0x9F),
    // Synth: Configure synth LDO (in ADI1, set SLDOCTL0.COMP_CAP=1)
    ADI_HALFREG_OVERRIDE(1,7,0x4,0x4),
    // Synth: Use 24 MHz XOSC as synth clock, enable extra PLL filtering
    (uint32_t)0x02010403,
    // Synth: Configure extra PLL filtering
    (uint32_t)0x00108463,
    // Synth: Increase synth programming timeout (0x04B0 RAT ticks = 300 us)
    (uint32_t)0x04B00243,
    // override_synth_disable_bias_div5.xml
    // Synth: Set divider bias to disabled
    HW32_ARRAY_OVERRIDE(0x405C,1),
    // Synth: Set divider bias to disabled (specific for loDivider=5)
    (uint32_t)0x18000200,
    // override_phy_rx_aaf_bw_0x0.xml
    // Rx: Set anti-aliasing filter bandwidth to 0x0 (in ADI0, set IFAMPCTL3[7:4]=0x0)
    ADI_HALFREG_OVERRIDE(0,61,0xF,0x0),
    // override_phy_gfsk_rx.xml
    // Rx: Set LNA bias current trim offset to 3
    (uint32_t)0x00038883,
    // Rx: Freeze RSSI on sync found event
    HW_REG_OVERRIDE(0x6084,0x35F1),
    // override_phy_gfsk_pa_ramp_5us_agc_reflevel_0x24.xml
    // Tx: Configure PA ramping setting (0x10) for approximately 5 us PA ramp time. Rx: Set AGC reference level to 0x24.
    HW_REG_OVERRIDE(0x6088,0x1024),
    // Tx: Configure PA ramping setting (0x08) for approximately 5 us PA ramp time
    HW_REG_OVERRIDE(0x608C,0x0813),
    // override_phy_rx_rssi_offset_5db.xml
    // Rx: Set RSSI offset to adjust reported RSSI by +5 dB (default: 0), trimmed for external bias and differential configuration
    (uint32_t)0x00FB88A3,
    // TX power override
    // Tx: Set PA trim to max (in ADI0, set PACTL0=0xF8)
    ADI_REG_OVERRIDE(0,12,0xF8),
    (uint32_t)0xFFFFFFFF
};


// CMD_PROP_RADIO_DIV_SETUP
// Proprietary Mode Radio Setup Command for All Frequency Bands
rfc_CMD_PROP_RADIO_DIV_SETUP_t RF_cmdPropRadioDivSetup =
{
    .commandNo = 0x3807,
    .status = 0x0000,
    .pNextOp = 0, // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
    .startTime = 0x00000000,
    .startTrigger.triggerType = 0x0,
    .startTrigger.bEnaCmd = 0x0,
    .startTrigger.triggerNo = 0x0,
    .startTrigger.pastTrig = 0x0,
    .condition.rule = 0x1,
    .condition.nSkip = 0x0,
    .modulation.modType = 0x1,
    .modulation.deviation = 0x2BC,
    .symbolRate.preScale = 0x6,
    .symbolRate.rateWord = 0x20000,
    .symbolRate.decimMode = 0x0,
    .rxBw = 0x2F,
    .preamConf.nPreamBytes = 0x4,
    .preamConf.preamMode = 0x0,
    .formatConf.nSwBits = 0x20,
    .formatConf.bBitReversal = 0x0,
    .formatConf.bMsbFirst = 0x1,
    .formatConf.fecMode = 0x0,
    .formatConf.whitenMode = 0x0,
    .config.frontEndMode = 0x2,
    .config.biasMode = 0x0,
    .config.analogCfgMode = 0x0,
    .config.bNoFsPowerUp = 0x0,
    .txPower = 0xA73F,
    .pRegOverride = pOverrides,
    .centerFreq = 0x0393,
    .intFreq = 0x8000,
    .loDivider = 0x05
};


// CMD_FS
// Frequency Synthesizer Programming Command
rfc_CMD_FS_t RF_cmdFs =
{
    .commandNo = 0x0803,
    .status = 0x0000,
    .pNextOp = 0, // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
    .startTime = 0x00000000,
    .startTrigger.triggerType = 0x0,
    .startTrigger.bEnaCmd = 0x0,
    .startTrigger.triggerNo = 0x0,
    .startTrigger.pastTrig = 0x0,
    .condition.rule = 0x1,
    .condition.nSkip = 0x0,
    .frequency = 0x0393,
    .fractFreq = 0x0000,
    .synthConf.bTxMode = 0x0,
    .synthConf.refFreq = 0x0,
    .__dummy0 = 0x00,
    .__dummy1 = 0x00,
    .__dummy2 = 0x00,
    .__dummy3 = 0x0000
};


// CMD_PROP_TX
// Proprietary Mode Transmit Command
rfc_CMD_PROP_TX_t RF_cmdPropTx =
{
    .commandNo = 0x3801,
    .status = 0x0000,
    .pNextOp = 0, // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
    .startTime = 0x00000000,
    .startTrigger.triggerType = 0x0,
    .startTrigger.bEnaCmd = 0x0,
    .startTrigger.triggerNo = 0x0,
    .startTrigger.pastTrig = 0x0,
    .condition.rule = 0x1,
    .condition.nSkip = 0x0,
    .pktConf.bFsOff = 0x0,
    .pktConf.bUseCrc = 0x1,
    .pktConf.bVarLen = 0x1,
    .pktLen = 0x14,
    .syncWord = 0x930B51DE,
    .pPkt = 0 // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
};


// CMD_PROP_RX
// Proprietary Mode Receive Command
rfc_CMD_PROP_RX_t RF_cmdPropRx =
{
    .commandNo = 0x3802,
    .status = 0x0000,
    .pNextOp = 0, // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
    .startTime = 0x00000000,
    .startTrigger.triggerType = 0x0,
    .startTrigger.bEnaCmd = 0x0,
    .startTrigger.triggerNo = 0x0,
    .startTrigger.pastTrig = 0x0,
    .condition.rule = 0x1,
    .condition.nSkip = 0x0,
    .pktConf.bFsOff = 0x0,
    .pktConf.bRepeatOk = 0x0,
    .pktConf.bRepeatNok = 0x0,
    .pktConf.bUseCrc = 0x1,
    .pktConf.bVarLen = 0x1,
    .pktConf.bChkAddress = 0x0,
    .pktConf.endType = 0x0,
    .pktConf.filterOp = 0x0,
    .rxConf.bAutoFlushIgnored = 0x0,
    .rxConf.bAutoFlushCrcErr = 0x0,
    .rxConf.bIncludeHdr = 0x1,
    .rxConf.bIncludeCrc = 0x0,
    .rxConf.bAppendRssi = 0x0,
    .rxConf.bAppendTimestamp = 0x0,
    .rxConf.bAppendStatus = 0x1,
    .syncWord = 0x930B51DE,
    .maxPktLen = 0xFF,
    .address0 = 0xAA,
    .address1 = 0xBB,
    .endTrigger.triggerType = 0x1,
    .endTrigger.bEnaCmd = 0x0,
    .endTrigger.triggerNo = 0x0,
    .endTrigger.pastTrig = 0x0,
    .endTime = 0x00000000,
    .pQueue = 0, // INSERT APPLICABLE POINTER: (dataQueue_t*)&xxx
    .pOutput = 0 // INSERT APPLICABLE POINTER: (uint8_t*)&xxx
};

  • 0
    TI__Guru**** 317180 points
    See 2.3 in www.ti.com/.../swra640a.pdf

    The optimal load for a single ended output is not 50 ohm and hence you get poor performance. You still need matching when you want to use a single ended solution.
  • 0 in reply to TER
    Expert 2330 points
    This is interesting but I'm a little bit confused:

    - first on page 7 of swra640a.pdf, I think that there is a mistake in the title of figure 1. Red is not required if *internal* bias is used (not external). Or is it?

    - secondly, on the CC1350STKEU_Schematics (1.5.0), if I use the internal bias, I don't have to install L15, C23. Correct?

    - thirdly, C14, C15, C16, L7 are fixed values to optimize the load of RF_N (both in emission and reception) to a 50-ohm antenna. Correct?
  • 0 in reply to GregoireGentil
    TI__Guru**** 317180 points
    - This is a typo, I have asked that it should be changed a couple of times... You are right, it should be internal in the text and not external.
    - That is correct
    - Yes

    Any reason why you want to go single ended vs using a IPC if you are space constrained?
  • 0 in reply to TER
    Expert 2330 points
    Right now, I have seen better range performance with single-ended despite zero matching rather than differential + IPC. Same software in both cases except the two settings mentioned at the top of this question.

    I have lost confidence in the IPC (see my other question) despite a correct routing of the IPC. It should give better performance but it doesn't. It might try Murata instead of Johanson but I'm not expecting something different.
  • 0 in reply to GregoireGentil
    TI__Guru**** 317180 points
    Ok, I suspect something strange with your IPC usage since you get very poor performance but we take that in the other thread on the topic.
  • 0 in reply to TER
    Expert 2330 points

    Still on this thread, how do you tune those passive components between the single-ended chip and the antenna? I know how to tune an antenna but I'm not sure how to do this in this case.

  • 0 in reply to GregoireGentil
    TI__Guru**** 317180 points

    Not sure what you mean. 

    The schematic from the CC1350STK:

    The components to the left for the red line is fixed and you don't need to change them (given that you operate in the 868 MHz/ 915 MHz band). The components to the right of the red line are the components that can be used for antenna tuning. Could you describe in more detail why you are not sure how to tune the antenna in this case? 

  • 0 in reply to TER
    Expert 2330 points

    I wanted to know from where those values were coming and how they were calculated (if I can reproduce in my lab). Are there the same for 868 and 915  (you seemed to say yes) but there are two schematics in swrc321a.zip marked US and EU and the US schematics has 868 (confusing)... There is another thread on E2E that gives completely different values for 400MHz so I was thinking that those values would have to be tuned per PCB/layout/frequency like for an antenna... You are implying the opposite (which is fine).

  • 0 in reply to GregoireGentil
    TI__Guru**** 317180 points
    The reason for the US/ EU marking is that the antenna on the STK has a bandwidth that only covers one band. Hence the components to the left of the red line are the same for both EU/ US but the antenna matching components are different.

    The matching network is also frequency dependent but one set of values covers both 868 MHz and 915 MHz/ give good performance for both bands. If you need a frequency outside these bands you also need to change the matching components.