AN31

AN31 SILABS | Alldatasheet

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manufacturing margin for frequency tuning. discrete “chip” inductor or a printed circuit board trace. recommended that a discrete “chip” inductor be used. the device pins as shown in Figure 1. Figure 1. Placement of Discrete described in the next section. the inductance is ±10% or better.

Rev. 1.3 3 4. Checking the Value of LEXT Once the desired inductor has been implemented, and the PCB has been fabricated, the value of L EXT should be verified. This can be done by following the steps listed below: 1. Measure the minimum operating frequency of the VCO in open-loop mode. This is accomplished by performing a sequence of register writes as described below. For the IF synthesizer: A. 0x000062 (hexadecimal)—power IF synthesizer and reference amplifier. B. 0x00024F—test register. C. 0x000F2D—test register. D. 0x010010—set the test bit in the main configuration register. E. 0x07FF1D—set the VCO to its minimum frequency. For the RF1 synthesizer: A. 0x000052 (hexadecimal)—power RF synthesizer and reference amplifier. B. 0x010003—dummy write to select RF1 synthesizer. C. 0x00024F—test register. D. 0x000F2D—test register. E. 0x010010—set the test bit in the main configuration register. F. 0x07FF0D—set the VCO to its minimum frequency. For the RF2 synthesizer: A. 0x000052 (hexadecimal)—power IF synthesizer and reference amplifier. B. 0x010004—dummy write to select RF2 synthesizer. C. 0x00024F—test register. D. 0x000F2D—test register. E. 0x010010—set the test bit in the main configuration register. F. 0x07FF0D—set the VCO to its minimum frequency. After programming the VCO to its minimum open- loop frequency, measure the value of fMIN. Note that this sequence of register writes leaves the device in a test mode. All the registers described in the data sheet should be re-written with normal values for proper closed-loop operation. 2. Measure the maximum operating frequency of the VCO in open-loop mode. This is accomplished by performing a sequence of register writes as described below. For the IF synthesizer: A. 0x000062 (hexadecimal)—power IF synthesizer and reference amplifier. B. 0x00024F—test register. C. 0x000F2D—test register. D. 0x010010—set the test bit in the main configuration register. E. 0x00001D—set the VCO to its maximum frequency. For the RF1 synthesizer: A. 0x000052 (hexadecimal)—power RF synthesizer and reference amplifier. B. 0x010003—dummy write to select RF1 synthesizer. C. 0x00024F—test register. D. 0x000F2D—test register. E. 0x010010—set the test bit in the main configuration register. F. 0x00000D—set the VCO to its maximum frequency. For the RF2 synthesizer: A. 0x000052 (hexadecimal)—power IF synthesizer and reference amplifier. B. 0x010004—dummy write to select RF2 synthesizer. C. 0x00024F—test register. D. 0x000F2D—test register. E. 0x010010—set the test bit in the main configuration register. F. 0x00000D—set the VCO to its maximum frequency. After programming the VCO to its maximum open- loop frequency, measure the value of fMAX. Note that this sequence of register writes leaves the device in a test mode. All the registers described in the data sheet should be re-written with normal values for proper closed-loop operation. 3. Calculate the measured center frequency for the synthesizer using Equation 7. fMEAS fMIN fMAX+ where fMEAS = measured center frequency

4 Rev. 1.3 fMIN = measure minimum frequency of operation fMAX = measured maximum frequency of operation 4. Calculate the measured external inductance, L MEAS, using Equation 8. LMEAS 2πfMEAS() C2 NOM where L MEAS = measured external conductance fMEAS = measured center frequency CNOM = nominal tank capacitance from synthesizer data sheet LPKG = package inductance from synthesizer data sheet 5. Refining the Implementation of Lext If the measured center frequency (f MEAS) is more than 2% away from the desired center frequency (f CEN), it is suggested that the external inductor be adjusted to provide maximum manufacturing margin. If the inductor is implemented with a discrete chip inductor, change the nominal value of this inductor using Equation LNEW 2LOLD LMEAS–= (Equation 9) where LNEW = nominal external inductance for next implementation LOLD = nominal external inductance from current implementation LMEAS = measured external inductance from current implementation If the inductor is implemented with a printed trace, change the D dimension of the trace using Equation 10. DNEW DOLD LCALC LMEAS– where DNEW = dimension shown in Figure 2 for next implementation in mm DOLD = dimension shown in Figure 2 from current implementation in mm LCALC = calculated value of external inductance from current implementation in nH LMEAS = measured external inductance from current implementation in nH X = constant of proportionality for MLP (XMLP) or TSSOP (XTSSOP) in nH/mm After the inductor has been adjusted, check the new value of L EXT as described in the previous section. 6. Example 1 Assume that the application requires the center frequency of the RF1 synthesizer on the Si4133-BM to be 1.6 GHz. The thickness of the dielectric is 210 µm. The first step is to calculate the required external inductance value, L EXT, from Equation 2: LEXT 2π1.6 10 9⋅() 4.3 10 12–⋅() Since the value is less than 3 nH, a printed trace implementation will be used. The constant of proportionality is calculated from Equation XMLP 0.620 1 0.823e 210– ⎛⎞ 0.519 nH /mm== Finally, from Equation 6: D 0.80 This is the calculated value in Table 1 for Figure 2, showing the appropriate printed trace inductor for this application. 7. Example 2 Assume that the application requires the center frequency of the IF synthesizer on the Si4133-BM to be 550 MHz. The thickness of the dielectric is 210 µm. The first step is to calculate the required external inductance value, L EXT, from Equation 2: EXT 2π550 10 6⋅() 6.5 10 12–⋅() Since the value is greater than 3 nH, a discrete “chip” inductor is recommended for the implementation. An inductor with a nominal value of 10.0 nH must be placed according to Figure 1 with the J dimension calculated by rearranging terms in Equation 3: J LEXT nH() LNOM nH()– 11.28 10.0– Note that the inductor must have a Q greater than 40 at 550 MHz, and the tolerance must be ±10% or better.

Rev. 1.3 5 8. Verifying Margin in Design Important: Please note that this proc edure is only intended for initial verification of the design of the board and external VCO tuning inductor. It is possible to determine the frequency tuning margin on a design implementation. This is accomplished by reading back from the synthesizer register values which indicate the tuning range of the VCOs using the following procedure: IF synthesizer: 1. Program the IF synthesizer to its highest frequency in the application. 2. Write 0x0001DE (hexadecimal) to enable a read of the IF tuning code. 3. Read 18 bits from the serial interface. (See “Serial Read Timing.") 4. The 18-bit value read from the interface is the tuning code. This value should be greater than 0x40 (hexadecimal) if the unit has adequate tuning margin. 5. Program the IF synthesizer to its lowest frequency in the application. 6. Write 0x0001DE (hexadecimal) to enable a read of the IF tuning code. 7. Read 18 bits from the serial interface. (See “Serial Read Timing.") 8. The 18-bit value read from the interface is the tuning code. This value should be less than 0x780 (hexadecimal) if the unit has adequate tuning margin. RF1 synthesizer: 1. Program the RF1 synthesizer to be active and at its highest frequency in the application. 2. Write 0x0000DE (hexadecimal) to enable a read of the RF tuning code. 3. Read 18 bits from the serial interface. (See “Serial Read Timing.") 4. The 18-bit value read from the interface is the tuning code. This value should be greater than 0x40 (hexadecimal) if the unit has adequate tuning margin. 5. Program the RF1 synthesizer to be active and at its lowest frequency in the application. 6. Write 0x0000DE (hexadecimal) to enable a read of the RF tuning code. 7. Read 18 bits from the serial interface. (See “Serial Read Timing.") 8. The 18-bit value read from the interface is the tuning code. This value should be less than 0x780 (hexadecimal) if the unit has adequate tuning margin. RF2 synthesizer: 1. Program the RF2 synthesizer to be active and at its highest frequency in the application. 2. Write 0x0000DE (hexadecimal) to enable a read of the RF tuning code. 3. Read 18 bits from the serial interface. (See “Serial Read Timing.") 4. The 18-bit value read from the interface is the tuning code. This value should be greater than 0x40 (hexadecimal) if the unit has adequate tuning margin. 5. Program the RF2 synthesizer to be active and at its lowest frequency in the application. 6. Write 0x0000DE (hexadecimal) to enable a read of the RF tuning code. 7. Read 18 bits from the serial interface. (See “Serial Read Timing.") 8. The 18-bit value read from the interface is the tuning code. This value should be less than 0x780 (hexadecimal) if the unit has adequate tuning margin. 8.1. Serial Read Timing In addition to the functions described in the data sheet, the AUXOUT pin can be used to read the contents of some synthesizer registers. By writing the values of 0x0001DE and 0x0000DE as described above, the serial interface is configured to read the tuning codes. During the readback, the function of the AUXOUT pin is to provide the serial data output from the device. Writing to any of the registers de scribed in the data sheet will cause the function of AUXOUT to revert to its previously programmed function. Th is is illustrated in Figure 4 below. Refer to Table 3 for timing values.

Figure 4. Read Timing Diagram Table 3. Serial Read Timing Values the synthesizer and the system in which it is to be used.

Rev. 1.3 7 NOTES:

8 Rev. 1.3 CONTACT INFORMATION Silicon Laboratories Inc.

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