Application Note Transceiver TH7122x Cookbook TH7122 and TH71221 Cookbook 1 General Description The TH7122 and TH71221 transceiver ICs are highly versatile ISM band RF components suitable for a wide range of applications. Both devices require external components for setting the operating frequency and IF bandwidth. The TH7122x, through proper component selection, may be used for any frequency between 27 and 950MHz. It performs well in wide and narrow band applications and with FM, FSK, and ASK (OOK) modulation. This application note is called a “Cookbook” because it is a tested collection of real applications and reference example circuits. The detailed descriptions of the procedures for selecting the appropriate components will help get your design up and running fast. 7 3 RSSI 2 VCC_IF 1 IN_IFA 31 VEE_IF 32 OUT_MIX IN_DEM 6 OUT_DEM PKDET SW1 1.5pF 26 MIX LNA 5 INT1 IFA SW2 OA1 Control Logic RO Fig. 1: 9 12 13 15 16 TE/SDTA 19 RE/SCLK 11 ASK/FSK VEE_PLL 10 RO IN_DTA 22 VEE_RO TNK_LO 20 VCC_PLL 23 LF FS1/LD 21 17 FS0/SDEN FSK FSK_SW PS_PA SCLK RO SDTA VCO 24 SCI R counter SDEN N counter PA 25 8 OUT_DTA 200k LO OUT_PA 4 INT2/PDO MIX IF ASK OA2 18 14 VCC_DIG IN_LNA bias FSK Demodulator VEE_DIG 30 IN_MIX 28 OUT_LNA 29 GAIN_LNA 27 VEE_LNA Please also consult the data sheets and evaluation board descriptions for detailed technical information. These can be found on the Melexis Web Site at www.melexis.com. Assistance and questions can be accessed using Melexis Knowledge Base Web Forum at www.melexis.com/forum. TH7122 and TH71221 IC block diagram 2 Important Features Usable in stand-alone or programmable user mode (via 3-wire bus serial control interface - SCI) The reference oscillator input (RO) can be a crystal oscillator or an input buffer from an external TCXO or microprocessor reference. It drives a programmable R counter with a range of 4 to 1023. The input range is 1 to 16MHz. The N counter has a very wide range of 64 to 131071, so very small VCO frequency steps are possible. The VCO is a negative resistance oscillator with a tuned circuit between pins 20 and 21. There is also an internal varactor (not shown). This allows the VCO to be tuned to any desired frequency by selecting the appropriate inductor. An external varactor can be added for wider tuning ranges. The loop filter for the VCO on pin 23 is external to allow optimizing the design for wide band or narrow band applications. The LNA and IF sections are tuned by external elements. Usually a ceramic filter is used for the IF, but crystal filters can be used for narrow band applications. The FM detector on pin 3 can be tuned with a ceramic discriminator or LC combination. OA1 is an operational amplifier to be configured as a data slicer OA2 is biased at Vcc/2 and can be used as an AFC amplifier. Both FSK and ASK (OOK) transmission and reception are possible with a switchable peak detector for ASK reception. ASK and FSK operation is possible without changing any parts by just loading in the correct control data via the SCI bus. 39011 07122 01 Rev. 004 Page 1 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook Document Content 1 General Description ...................................................................................................1 2 Important Features.....................................................................................................1 3 VCO Design ................................................................................................................4 4 5 6 3.1 Standard FSK VCO .......................................................................................................... 4 3.2 Standard ASK VCO .......................................................................................................... 5 3.3 VCO with External Varactor.............................................................................................. 5 Modulation ..................................................................................................................6 4.1 FSK Crystal Modulation .................................................................................................... 6 4.2 Analog FM or FSK ............................................................................................................ 6 4.3 Direct VCO Modulation for Narrow Band.......................................................................... 7 4.4 High Speed Data Communication .................................................................................... 7 4.5 FSK Modulation – AC-Coupling........................................................................................ 8 4.6 Two Point FSK Modulation ............................................................................................... 8 4.7 Multi-Band Switching ........................................................................................................ 9 IF Filtering...................................................................................................................9 5.1 IF Filter - Standard.......................................................................................................... 10 5.2 IF Ceramic Filter - Narrow Band ..................................................................................... 10 5.3 IF Crystal Filter - Narrow Band ....................................................................................... 10 FSK and FM Detectors .............................................................................................11 6.1 FSK Detector - Standard ................................................................................................ 11 6.2 FSK Detector – LC Tank ................................................................................................ 11 6.3 High Speed FSK Detector .............................................................................................. 12 6.4 FSK Detector - External AFC (I) ..................................................................................... 12 6.5 FSK Detector - External AFC (II) .................................................................................... 13 6.6 FSK Squelch Circuit ....................................................................................................... 13 6.7 FM Detector .................................................................................................................... 14 6.8 Wide Band FSK / ASK Detector ..................................................................................... 14 6.9 High Performance Narrow Band Receiver Using External IF IC .................................... 15 6.9.1 7 Component List for Fig. 2........................................................................................................... 16 ASK (OOK) Detectors and RSSI ..............................................................................17 7.1 ASK Detector - Standard ................................................................................................ 18 7.2 ASK Detector - Peak Detector ........................................................................................ 18 39011 07122 01 Rev. 004 Page 2 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 8 RF Input Matching ....................................................................................................19 9 RF Output Matching .................................................................................................19 10 LNA Output and Mixer Input Matching ...................................................................20 11 Special Considerations............................................................................................20 12 EVB7122 Special Evaluation Board ........................................................................21 12.1 Circuit Schematic Direct VCO Modulation for Narrow Band with SAW Filter ................. 22 12.1.1 12.2 Component Arrangement Top Side for schematic 12.1......................................................... 23 Circuit Schematic High Speed Data Communication ..................................................... 24 12.2.1 Component Arrangement Top Side for schematic 12.2......................................................... 25 12.3 Circuit Schematic 433MHz - NB - 10.7MHz ext. IF......................................................... 26 12.4 Circuit Schematic 868MHz - NB - 21.4MHz ext. IF......................................................... 27 13 Overview Component List for Special Boards ......................................................28 14 Special Board Layouts.............................................................................................30 39011 07122 01 Rev. 004 Page 3 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 3 VCO Design If the internal varactor diode of the TH7122x is used for tuning the VCO at Vcc = 3.0V, the tuning ratio is fmax / fmin ≤ 1.135. For Vcc = 5.0V, the ratio is approximately 1.191. This determines whether or not an external varactor is required. For example, at 27MHz operation with a 10.7MHz IF (intermediate frequency), the VCO frequency in the receiver will be 37.7MHz. This gives fmax / fmin = 1.40, so an external varactor will be required. Tuning ratios up to 2:1 are possible with hyper-abrupt tuning diodes. Another consideration when tuning the VCO is the tuned circuit impedance. The VCO is a negative resistance oscillator, and its resistance decreases with increasing frequency. Its noise can be improved by reducing the tank circuit losses to increase the Q of the tank. The loaded Q of the equivalent RLC parallel combination of the VCO tank is R / L/C . It is limited by the parasitic elements of the IC package and the PCB. Care must be taken not to make the tank inductor too small, the VCO may not start or may oscillate at a high parasitic frequency which is determined by the circuit traces and stray capacitance of the coil and/or varactor circuit. On the other hand, the coil inductance must be small in order to have a low tuned circuit impedance ( L / C ) . This means that the tuning capacitance should be large. In this case, an external varactor must be used even though the same frequency could be tuned with the internal varactor. With a tuning voltage range from 0.2V to Vcc - 0.2V, the equivalent capacitance Cint across pins 20 and 21 is approximately 3.37 to 4.34pF when Vcc = 3.0V. When Vcc = 5.0V, the minimum capacitance is approximately 3.06pF. The VCO directly generates the RF signal in transmit mode, so the VCO and transmit (carrier) frequency are the same. In receive mode, the VCO is also active and its frequency is offset from the receive frequency by the IF (because of the super-heterodyne receiver architecture). In this mode the VCO is also called LO (local oscillator). There is always a slight LO signal passing to the receiver input. This undesired leakage is lowest if the VCO current is set to the smallest value; this can be done by setting the VCOCUR register bits to 00. VCC 1nF RF C0 FS1/LD 19 VEE_DIG 18 TNK_LO 21 VCC_PLL 20 LF 23 VEE_PLL 22 24 L0 OUT_PA 100pF CB6 17 FS0/SDEN RPS 25 3.1 Standard FSK VCO CF1 33k CF2 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 IN_DEM INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 IN_IFA 1 39011 07122 01 Rev. 004 VCC_IF RO 10 32 OUT_MIX 3 31 VEE_IF 2 30 IN_MIX FSK_SW 11 RF, CF1 and CF2 are the values used on the standard evaluation boards (EVBs). C0 can be added to adjust the VCO tuning voltage that can be monitored on pin 23 so it is not too close to Vcc or GND. This way the VCO frequency can be centered for optimum performance in the particular operating range. This circuit is recommended for data rates up to about 20kbps NRZ (non-return to zero). The FSK modulation is achieved by switching the capacitive loading of the crystal oscillator, just as shown in the TH7122x data sheets. 9 VEE_RO Page 4 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook RB0 VCC 100 3.2 Standard ASK VCO CF1 39pF 100pF C0 FS1/LD 19 VEE_DIG 18 TNK_LO 21 OUT_PA VCC_PLL 20 VEE_PLL 22 L0 LF 23 24 RPS 25 RF CPS 1nF 100pF CB6 17 FS0/SDEN 33k CF2 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA OUT_DEM RSSI OUT_DTA 8 INT1 5 7 INT2/PDO 4 6 IN_DEM IN_IFA 1 3 RO 10 VCC_IF 31 VEE_IF 2 FSK_SW 11 9 VEE_RO RB0 VCC 100 3.3 VCO with External Varactor RF This circuit can be used to extend the frequency range. The frequency extension can be even down to 27MHz. CF2 CF1 C01 10k 22 RF1 VD1 R01 FS1/LD 19 VEE_DIG 18 TNK_LO 21 VCC_PLL 20 VEE_PLL 22 LF 23 24 100pF C0 L0 OUT_PA The VCO frequency fvco is given by: CB6 17 FS0/SDEN RPS 25 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 IN_IFA 1 IN_DEM RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 39011 07122 01 Rev. 004 f VCO = 1 2π 1 Cd ⋅ C01 ⎞ ⎛ L0⎜ C0 + Cint + ⎟ Cd + C01 ⎠ ⎝ Where Cint = internal diode capacitance Cd = diode capacitance of VD1 RF1 connects the varactor to the tuning voltage and filters the RF signal present on the diode. ASK/FSK 13 TH7122x 29 GAIN_LNA 32 OUT_MIX CPS also helps to minimize spurious FM by reducing the rise and fall time of the PA switching on and off. IN_DTA 12 30 IN_MIX 32 OUT_MIX C0 is added to reduce the tuning range of the VCO. This results in smaller frequency disturbances (spurious FM) caused by switching the PA stage on and off. ASK/FSK 13 TH7122x 29 GAIN_LNA RF, CF1 and CF2 are set to give a wider PLL bandwidth. This allows the VCO to correct faster for frequency disturbances caused by load pulling effects in the ASK-modulated PA. 9 VEE_RO R01 is used in low frequency applications to prevent parasitic oscillations at high frequencies. It is also possible to put R01 in series with pin 20. The combination of C0 and C01 set the tuning range. If VD1 has a large capacitance at 0V, C01 should not be made larger than about 100pF or the low impedance of the circuit may prevent start-up of the VCO. Page 5 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook The selection of RF, CF1, CF2 is important for good FSK and ASK modulation. These values depend on the PLL counter values, the maximum modulating frequency and the desired phase margin. The design equations for the loop filter are in the Melexis application note: TH7122 and TH71221x Used in Narrow Band FSK Applications. A value for M = 2.5 the phase margin will be approximately 45 degrees. This results in a fast rise time with some overshoot in the FSK signal, but this overshoot is usually filtered out in the receiver. In ASK applications, the ASK spectrum is improved because the VCO returns to the center frequency faster with no ringing. The easiest way to design the filter is to select 39pF for CF2 and then design RF and CF1 to give the desired damping. This gives the widest possible loop bandwidth for good FSK and ASK operation. For this condition, the highest possible loop comparison frequency should be used. 4.1 FSK Crystal Modulation 17 FS0/SDEN VEE_DIG 18 FS1/LD 19 VCC_PLL 20 4 Modulation This is the standard approach to generate an FSK signal. The crystal frequency, that provides the reference to the internal PLL synthesizer, is pulled by two external capacitors CX1 and CX2. An internal switch at pin FSK_SW is either open (if the signal at pin IN_DTA is logic high) or connected to ground (if the signal at pin IN_DTA is logic low). This way either CX1 or the combination of CX1 + CX2 determines the crystal frequency. So the FSK signal is generated at the crystal frequency and then up-converted in the PLL. 16 RE/SCLK 15 VCC_DIG 14 ASK/FSK 13 mod IN_DTA 12 FSK_SW 11 CX2 CX1 INT1 OUT_DEM RSSI OUT_DTA 5 6 7 8 RO 10 9 VEE_RO XTAL The polarity of the signal at IN_DTA can also be inverted in programmable mode. 17 FS0/SDEN VEE_DIG 18 FS1/LD 19 VCC_PLL 20 This circuit is recommended for data rates ranging from DC to about 20kbps NRZ. 4.2 Analog FM or FSK In this circuit a varactor diode is used to modulate the crystal. An external 2nd order Sallen-Key low-pass filter can be added to shape the modulating signal. 16 RE/SCLK 15 VCC_DIG 14 ASK/FSK 13 IN_DTA 12 CX1 VD2 XTAL 100k OUT_DTA 9 VEE_RO C 8 RSSI RO 10 7 OUT_DEM 6 5 INT1 FSK_SW 11 X mod R R C The filter cut-off frequency is given by: A1 fC = mod X R C 39011 07122 01 Rev. 004 The easiest Sallen-Key setup is to use equal filter resistors and equal capacitors. This makes the filter cutoff frequency and the Q independent of one another. Direct feedback from the A1 output to the (-) input creates a unity-gain characteristic. If the requirements for filtering are low, a very simple passive RC filter can be used instead. 1 2π ⋅ RC The circuit can be used, for example, to transmit audio signals. Page 6 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook mod RB0 VCC RM3 CM1 RF CM2 RM1 CF2 10k 100 1M CF1 10k RM2 C01 RF1 VD1 100pF C0 CB6 FS1/LD 19 VEE_DIG 18 TNK_LO 21 LF 23 OUT_PA VCC_PLL 20 25 VEE_PLL 22 24 L0 17 FS0/SDEN RPS 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT1 OUT_DEM RSSI OUT_DTA 6 7 8 INT2/PDO 5 4 IN_IFA 1 32 OUT_MIX IN_DEM RO 10 VCC_IF 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 9 VEE_RO 4.3 Direct VCO Modulation for Narrow Band This circuit is usually used in narrow band applications. Rather than switching the crystal oscillator’s capacitive loading for FSK generation, this circuit employs socalled direct VCO modulation. This means data is directly injected into the VCO control line through the loop filter. CF1 is usually 1.0µF or larger and CF2 is usually 100nF or larger. RF is usually around 1.5 to 3.3kΩ. To get flat modulation response, it is necessary that CM1·RM1 = CF2·RF. Since the VCO is very sensitive, the modulation signal must be attenuated. RM1 = 1MΩ and RM3 = 10kΩ for convenience, and the modulation sensitivity is adjusted by changing RM2. CM2 can be added to reduce the rise time of the digital modulating signal to reduce the occupied bandwidth. This arrangement can also be used with only the internal varactor. The design equations for the loop filter are in the Melexis application note: TH7122 and TH71221 Used In Narrow Band FSK Applications VCC 4.4 High Speed Data Communication CM1 RF CF2 mod RM1 CF1 100pF FS1/LD 19 VEE_DIG 18 TNK_LO 21 VCC_PLL 20 OUT_PA VEE_PLL 22 25 LF 23 24 L0 17 FS0/SDEN CB6 RPS The design equations for the loop filter are in the Melexis application note TH7122 and TH71221 High Speed Data Communication. 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 IN_IFA 1 39011 07122 01 Rev. 004 IN_DEM RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 32 OUT_MIX This circuit is usually used in high speed applications for data rates of up to about 115kbps NRZ. It is similar to the preceding one and also employs direct VCO modulation. But here no external varactor is needed. 9 VEE_RO Page 7 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 100 CF1 CF2 10k CB6 17 FS0/SDEN FS1/LD 19 VEE_DIG 18 TNK_LO 21 VCC_PLL 20 24 LF 23 VEE_PLL 22 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 IN_DEM INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX IN_IFA 1 32 OUT_MIX 9 VEE_RO VCC 100 CF1 RB0 RM1 mod CM1 RF 10k C01 RF1 VD1 RPS 100pF C0 CB6 VEE_DIG 18 FS1/LD 19 TNK_LO 21 VCC_PLL 20 OUT_PA VEE_PLL 22 24 LF 23 L0 17 FS0/SDEN CF2 25 This method accomplishes the same result as in section 4.3 but with fewer components and no additional current when in standby mode. CM1 and CF1 form a capacitive divider to set the modulation sensitivity. RM1 is added to reduce the high frequency response to reduce the modulation bandwidth 100pF C0 L0 28 OUT_LNA 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 IN_IFA 1 IN_DEM RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 32 OUT_MIX 39011 07122 01 Rev. 004 4.5 FSK Modulation – AC-Coupling C01 RPS OUT_PA VCC CM1 RF RF1 VD1 25 RB0 mod RM1 4.6 Two Point FSK Modulation When the VCO is modulated, it has a highpass response due to the nature of the PLL. Because of this, it is necessary to have a lower loop frequency which is about 1/3 of the lowest modulating frequency. In the case of FSK modulation, long data pulses will become distorted as the loop forces the VCO back to the center frequency. The common way to deal with this is to apply the data pulses to the reference so that it is also modulated. This can be done with a varactor on the crystal reference as in section 4.2 or by using FSK crystal modulation as in section 4.1. The lowest cost method is FSK crystal modulation using a small capacitance for CX2. This does not result in a perfect frequency crossover between VCO and crystal modulation but in most cases the result is satisfactory. CX2 In the circuit shown, the crystal modulation is out of CX1 phase with the VCO modulation, so the DTAPOL setting for the TH7122 must be set to ‘1’ – inverse. 9 VEE_RO XTAL Page 8 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook RB0 VCC L03 1µH RF R03 C03 BBY65 22 CF2 100pF CF1 VD1 RF1 10k 27nH RPS CB6 RS1 1nF PD1 470 BS1 C02 L02 BAR64 330pF RS2 470 PD2 L01 BS2 C01 2.2nH 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 IN_DEM INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 5 6 7 8 IN_IFA 1 4 RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 32 OUT_MIX This circuit shows one method for switching the VCO bands to cover a wider tuning range. In this case, the lowest frequency is around 27MHz and the highest is 950MHz. PD1 and PD2 are PIN diodes with a low capacitance at 0V. VD1 is a wide range tuning diode. BS1 and BS2 are the band switching inputs. R03 prevents parasitic oscillations when the low frequencies are selected. When BS1 and BS2 = Vcc, the lowest frequency is set by L02 and L03, VD1 and the TH7122x internal varactor. 17 FS0/SDEN FS1/LD 19 VEE_DIG 18 VCC_PLL 20 TNK_LO 21 OUT_PA VEE_PLL 22 LF 23 BAR64 100pF 24 25 4.7 Multi-Band Switching 22 9 VEE_RO When BS1 = 0V, and BS2 = Vcc, the low frequency circuit is shorted by PD1, and the frequency is determined by LO2 and the TH7122x internal varactor. This setting is for medium bands. When BS1 = Vcc and BS2 = 0V, the frequency is determined by LO1 and the TH7122x internal varactor. This is the highest frequency band setting. Remember that the off capacitance of the PIN diodes is in parallel with the coils and the series inductance of the PIN diode and C01/02 adds to the coil inductance and becomes significant. Also, the drive to BS1, and BS2 must be able to sink approximately 10mA at Vcc = 5V. 5 IF Filtering LC, ceramic or crystal filters can be used for the IF filter. The most common frequency for this type of application is 10.7MHz. 21.4MHz IF filters can also be used. 455 or 450kHz is not practical because the internal capacitor coupling the IF to the demodulator is only 1.5pF. Also, with single conversion and a low IF, the receiver has virtually no image rejection. The output resistance of pin 32, OUT_MIX, is about 330Ω to match most ceramic filters. In order to match other filters, a passive matching network can be used. A simple PI or L matching network can be used, but a PI network with a higher Q has the advantage of reducing the spurious responses of the filter far from the center frequency. A PI network can also be added to the normal ceramic wide band filter to suppress spurious responses. The input resistance of pin 1, IN_IFA, is about 2kΩ in parallel with a few pF of capacitance. This is very convenient because this is about the required termination for 10.7MHz crystal filters. Just adding a resistor between pins 1 and 2 can terminate filters which require a smaller load resistance of for example 330Ω. In the normal application, the IF filter is the same as the ones used in most FM radio receivers. Its bandwidth is usually around 180kHz, but the FSK deviation in most ISM applications is usually around 30kHzpk-pk. Therefore, it is not necessary to terminate the filter with 330Ω to keep the response flat, so the resistor at IN_IFA can be omitted. The IF amplifier 3dB low and high end frequencies are about 400kHz and 30MHz, respectively and the –3dB sensitivity at 10.7MHz is about 150µV with a ceramic discriminator. 39011 07122 01 Rev. 004 Page 9 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 5.1 IF Filter - Standard 30 IN_MIX This filter circuit can be used with all types of filters. For all 330Ω filters. , it can be used to suppress filter responses far from the center frequency: LIF = 2.2µH, CIF1 = CIF2 = 200pF, RIF = 390Ω IN_DEM 3 2 IN_IFA 1 CERFIL VCC_IF 31 VEE_IF 32 OUT_MIX VCC CB5 100nF SMD type ceramic filters from Murata are for example or equivalent part: SFECV10.7MJA00 @ BIF = 150 kHz (size 7x3mm) SFECV10.7MHA00 @ BIF = 180 kHz (size 3.5x3.1mm) 5.2 IF Ceramic Filter - Narrow Band 30 IN_MIX IN_DEM If a NB ceramic filter with 600Ω is used , then some additional components are recommended: LIF1 = 2.2µH, CIF1 = 180pF, CIF2 = 220pF, RL0 = 820Ω 3 2 IN_IFA 1 CERFIL CIF1 CIF2 LIF1 32 OUT_MIX VCC_IF 31 VEE_IF RL0 VCC 100nF CB5 A leaded type ceramic filter from Murata is for example or equivalent part: SFKLA10M7NL00 @ BIF = 30 kHz 5.3 IF Crystal Filter - Narrow Band 30 IN_MIX If a crystal filter with 3kΩ termination is used then the additional components should be: LIF1 = 10µH, CIF1 = 22pF, CIF2 = 3.9pF FIL2 22pF 3.9pF FIL1 CIF1 CIF2 IN_DEM 3 2 LIF1 10µH IN_IFA 1 32 OUT_MIX VCC_IF 31 VEE_IF VCC 100nF CB5 Remember that a single 2-pole crystal filter has a maximum attenuation of only 25dB, so a 4-pole filter should be used for best results. One half (2 poles) of 4-pole crystal filter from ECS is for example: ECS-10.7-7.5B @ BIF = 7 kHz 39011 07122 01 Rev. 004 Page 10 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 6 FSK and FM Detectors 17 FS0/SDEN FS1/LD 19 VEE_DIG 18 VCC_PLL 20 TNK_LO 21 OUT_PA VEE_PLL 22 24 25 LF 23 The FM detector is an analog detector. The detector output signal can be observed on pin 6. If the TH7122x is used in a tone or voice application, this signal would go to a tone decoder or audio amplifier. 6.1 FSK Detector - Standard RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DEM INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 10nF 100nF CB5 9 VEE_RO OUT_DTA 330pF IN_IFA 1 3 RO 10 VCC_IF 31 VEE_IF 2 FSK_SW 11 C3 Any ceramic discriminator can be used with the TH7122x by adjusting CP. The range is usually about 9 to 15pF. IN_DTA 12 30 IN_MIX 32 OUT_MIX The normal ceramic discriminator FM detector acts like a high Q coil. CP is used to tune it, and RP is used to set the detector bandwidth. 16 26 IN_LNA OUT_DEM RSSI C4 CP C5 1.5nF 10nF CERDIS CB4 17 FS0/SDEN FS1/LD 19 VCC_PLL 20 VEE_DIG 18 VCC TNK_LO 21 OUT_PA VEE_PLL 22 25 LF 23 24 RP 27 VEE_LNA VCC_DIG 14 29 GAIN_LNA ASK/FSK 13 IN_DTA 12 100nF CB5 INT1 OUT_DEM RSSI OUT_DTA 5 6 7 8 10nF C3 330pF IN_DEM INT2/PDO IN_IFA 1 4 RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 32 OUT_MIX 9 VEE_RO 10nF CB4 CP f IF = OUT_DEM 1 1 2π LDIS ⋅ CP RSSI C4 LDIS 6.8µH VCC 39011 07122 01 Rev. 004 This circuit shows how the ceramic discriminator can be replaced by an LC tank. CP and LDIS are forming a parallel resonant circuit and so the formula to calculate the desired IF follows this equation: OUT_DTA C5 1.5nF 33pF An adjustable coil or fixed coil with a trimmer capacitor can be substituted for the ceramic discriminator. In this case, RP may not be needed because the coil Q will be low. 16 RE/SCLK 15 TH7122x The TH7122x features an internal AFC circuit. It is disabled by default in stand-alone user mode and can be activated in programmable user mode. The AFC allows the receiver to track on frequency variations of the transmitter. The receiver tracking range depends on the FSK deviation (∆f), it’s about ± 100kHz at ∆f = ± 20kHz. 6.2 FSK Detector – LC Tank 26 IN_LNA 28 OUT_LNA The detector bandwidth is set by the demodulator output resistance of 270kΩ and the external capacitor C4. An LC discriminator can be used to setup the IF circuit for any desired frequency within the range of 0.4 to 22MHz if no standard ceramic discriminator is available. Page 11 of 32 AN7122x-Cookbook Dec./05 Application Note 17 FS0/SDEN VEE_DIG 18 FS1/LD 19 VCC_PLL 20 LF 23 OUT_PA TNK_LO 21 25 VEE_PLL 22 24 Transceiver TH7122x Cookbook 6.3 High Speed FSK Detector 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 OUT_DTA C3 1.5nF 100k 100k RL1 C5 RP CB4 C4 17 FS0/SDEN VEE_DIG 18 VCC FS1/LD 19 VCC_PLL 20 TNK_LO 21 LF 23 OUT_PA VEE_PLL 22 24 CERDIS 25 6.4 FSK Detector - External AFC (I) RE/SCLK 15 27 VEE_LNA VCC_DIG 14 ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT1 OUT_DEM RSSI OUT_DTA 5 6 7 8 CB5 100pF 10nF CB4 39011 07122 01 Rev. 004 RP CERDIS CP CS 100k R3 C4 100nF C3 330pF INT2/PDO 4 10nF IN_IFA 1 IN_DEM RO 10 VCC_IF 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 32 OUT_MIX An external AFC circuit can be added to the ceramic discriminator or a coil to further increase the detection range. This is useful when working with SAW transmitters which may have a frequency tolerance up to 200kHz. The AFC time constant is determined by the demodulator output resistance of 270kΩ times C3. Be sure to turn on OA2 in the TH7122x when using this circuit. The capacitance across CERDISC is: 16 26 IN_LNA 28 OUT_LNA The design equations for the detector are in the Melexis application note TH7122 and TH71221 High Speed Data Communication. RSSI OUT_DEM 10nF 100nF CB5 10nF Note that RL1 and RL2 are AC-wise put in parallel. 9 VEE_RO RL2 IN_IFA 1 IN_DEM RO 10 VCC_IF 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 32 OUT_MIX If the transmit part of the receiver is setup for high speed, according to para. 3.5, then the receiver should be as well. This can be done by adding two resistors RL1 and RL2 at the output of the demodulator. They are reducing the IC’s output impedance (which is about 270kΩ) and so the cut-off frequency is increased. 16 9 VEE_RO OUT_DTA CS ⋅ Cd CS + Cd OUT_DEM Where Cd is the diode capacitance. RSSI C5 1.5nF CP + With this circuit the tracking range can be further increased (compared to the circuit in 6.1) VD2 VCC Page 12 of 32 AN7122x-Cookbook Dec./05 Application Note 17 FS0/SDEN VEE_DIG 18 FS1/LD 19 VCC_PLL 20 LF 23 OUT_PA TNK_LO 21 25 VEE_PLL 22 24 Transceiver TH7122x Cookbook 6.5 FSK Detector - External AFC (II) 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 100pF 100k R3 CB5 C3 CS LDIS 10nF OUT_DTA OUT_DEM RSSI C5 1.5nF VD2 6.8µH CB4 C4 100nF 9 VEE_RO 330pF 10nF IN_IFA 1 IN_DEM RO 10 VCC_IF 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 32 OUT_MIX For really wide detection ranges (of about ± 150 to 250kHz), a coil tuned discriminator can be used together with the external AFC. In this circuit, if VD2 is a BB639 diode, it will tune the 6.8µH coil. The tuning can be adjusted by changing C7 and/or by adding another CP in parallel with LDIS. 16 17 FS0/SDEN VEE_DIG 18 FS1/LD 19 VCC_PLL 20 LF 23 OUT_PA TNK_LO 21 25 VEE_PLL 22 24 VCC 6.6 FSK Squelch Circuit 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT1 OUT_DEM RSSI OUT_DTA 5 6 7 8 100nF CB5 10nF C3 330pF INT2/PDO 4 IN_IFA 1 32 OUT_MIX IN_DEM RO 10 VCC_IF 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 9 VEE_RO OUT_DTA OUT_DEM The circuit diagram shows how squelch functionality can be added to the standard FSK application circuit. The RSSI output is used to detect an RF signal at the receiver input IN_LNA. In case an RF signal is available, the RSSI signal goes up to a certain voltage level. The absolute voltage level depends on the actual RF input level. This DC voltage level can be adjusted with the potentiometer RSQ1 before it passes the resistor RSQ2. Now this voltage is used to set the threshold of the comparator OA1 by feeding it to pin INT1.The impedance of RSQ1 and RSQ2 must be lower than the output impedance at OUT_DEM plus the internal 200kΩ resistor at the (-) input of OA1 to “overwrite” the DC content from the demodulator output. RSSI C4 C5 1.5nF RSQ1 220k 10nF CB4 RP 39011 07122 01 Rev. 004 15k CERDIS RSQ2 VCC Page 13 of 32 AN7122x-Cookbook Dec./05 Application Note 17 FS0/SDEN FS1/LD 19 VEE_DIG 18 6.7 FM Detector 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT1 OUT_DEM RSSI 5 6 7 OUT_DTA RSSI 1.5nF C CB5 R C A2 RP 10nF CB4 17 FS0/SDEN VEE_DIG 18 27 VEE_LNA VCC_DIG 14 ASK/FSK 13 TH7122x IN_DTA 12 39011 07122 01 Rev. 004 OUT_DEM RSSI 6 7 RP CERDIS CP 680k 100pF CB4 OUT_DTA INT1 5 100k CS 10nF Vcc + 0.45 2 8 IN_DEM R1 100nF CB5 9 VEE_RO OUT_DTA C6 2 IN_IFA 1 100nF INT2/PDO RO 10 4 31 VEE_IF 3 FSK_SW 11 VCC_IF 30 IN_MIX 32 OUT_MIX The circuit is useful, for example, to receive audio signals. It is complementary to the FM transmit circuit shown in para. 4.2. If the ASK peak detector and the FSK detector with AFC are required in one application, the AFC circuit can be driven from the OUT_DEM like this. R8 and C10 filter out the audio or data signal from OUT_DEM. R9 is to decouple the RF signal on the diode from CS. The output swing on pin 8 is from about 0.7V to Vcc -0.25V so the diode should be set up so CERDIS is tuned to the center frequency at: 16 RE/SCLK 15 29 GAIN_LNA 1 2π ⋅ RC 6.8 Wide Band FSK / ASK Detector 26 IN_LNA 28 OUT_LNA fC = VCC FS1/LD 19 VCC_PLL 20 TNK_LO 21 OUT_PA VEE_PLL 22 LF 23 24 CERDIS 25 The simplest setup is to use equal filter resistors and equal capacitors. This makes the filter cut-off frequency and the Q independent of one another. Direct feedback from the A2 output to the (-) input creates a unity-gain characteristic. The filter cut-off frequency is given by: C5 R 100nF 9 VEE_RO 8 INT2/PDO 4 IN_IFA 1 IN_DEM RO 10 3 31 VEE_IF VCC_IF FSK_SW 11 2 30 IN_MIX 32 OUT_MIX This circuit can be applied to process FM signals at the demodulator output. An external Sallen-Key low-pass filter is used to band-limit the output signal. 16 OUT_FM TNK_LO 21 OUT_PA VCC_PLL 20 VEE_PLL 22 24 25 LF 23 Transceiver TH7122x Cookbook C5 1.5nF OUT_DEM R2 R9 33k VD2 R8 1M C10 100nF C4 330pF VCC Page 14 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 6.9 High Performance Narrow Band Receiver Using External IF IC Below is a narrow band IF circuit using an IF IC from NJR. Several other manufacturers make a similar part for this type of application. The external IF IC gets the input signal from the TH7122x mixer output. Matching components for a 600Ω ceramic filter and crystal filters are shown. Resistors R8, R14, R17 are for setting different FSK options. R18, R19 are used for setting the carrier sense level. FL1 is a 6 pole crystal filter for 12.5 or 25kHz channels. IF frequencies up to 45MHz can be used with this circuit together with any of the narrow band VCO circuits for the TH7122. The additional current drain is only 1.5 to 2mA. Since this narrow band IF is very sensitive, the LNA gain in the TH7122 can be reduced to improve the intermodulation rejection. IF1 1 2 IF_IN GND LF1 CF2 to Pin 32 TH7122x OUT_MIX VCC R1 CX2 1 2 C2 CB0 CB1 CERDIS C3 OSC8 MIXIN 20 OSCE 19 3 MIXOUT SENSLVL 18 4 VCC RSSIOUT 17 5 IFIN CARSENSE 16 6 DEC FSKOUT 15 7 FSKREF1 CHGSW 14 8 FSKREF2 LPFOUT 13 9 IFOUT LPFIN 12 10 QUAD AFOUT 11 RP U1 R3 R2 R4 C4 C5 R5 C7 C6 R6 R7 CARRIER FSK_DTA GND 3 2 1 C1 1 2 3 2 1 VCC IF2 VCC GND FIL1 XTAL CX1 FIL2 RL0 CF1 AF_OUT RSSI GND CP Fig. 2: TH7122x external NB IF Two receivers were designed to use with the NB IF shown above. One operates at 433MHz with 25kHz channel steps and the other operates at 868MHz. The 868MHz one does not use an external varactor, but C0 is large to reduce the VCO sensitivity. The performance with this combination is impressive. 433MHz receiver: ∆f = ±3kHz, data rate 2kbps NRZ, BER = 3⋅10 868MHz receiver: -3 ∆f = ±3kHz, data rate 2kbps NRZ, BER = 3⋅10-3 input sensitivity = -120dBm input sensitivity = -120dBm max S/N = 40dB max S/N = 34dB ±25kHz channel selectivity = 47dB ±25kHz channel selectivity = 40dB ±50kHz channel selectivity = 55dB ±50kHz channel selectivity = 48dB 39011 07122 01 Rev. 004 Page 15 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 6.9.1 Component List for Fig. 2 Part Size Value IF1 @ 10.7MHZ Value IF1 @ 21.4MHz NMJ2593 NMJ2593 Description C1 0805 100 nF 100 nF 50 MHz input mixer and 450/455 kHz FM IF demodulator IC IF decoupling C2 C3 C4 C5 C6 C7 0805 0805 0805 0805 0805 0805 100 nF 82 pF 1 nF 15 nF 1 nF 560 pF 100 nF 82 pF 1 nF 15 nF 1 nF 560 pF data slicer capacitor when using CDBLA455KCAY07 CERDISC RSSI output low pass capacitor part of HPF for audio output part of active LPF part of active LPF CB0 CB1 CF1 CF2 CP CX1 CX2 1210 0805 0805 0805 0805 0805 0805 10 uF 100 nF 27 pF 68 pF 15 pF 39 pF 56 pF 10 uF 100 nF 33 pF 82 pF 15 pF 39 pF 56 pF De-coupling capacitor De-coupling capacitor For crystal filters For crystal filters when using CDBLA455KCAY07 CERDISC For XTAL1 with 32 pF load For XTAL1 with 32 pF load LIF1 R1 1008 0805 10 µH 2.2 µH 100 kΩ 100 kΩ for crystal filters sets carrier sense level R2 0805 33 kΩ 33 kΩ sets carrier sense level R3 0805 100 kΩ 100 kΩ collector load for FSK out R4 0805 100 kΩ 100 kΩ collector load for carrier sense out R5 0805 100 kΩ 100 kΩ part of active LPF R6 0805 100 kΩ 100 kΩ part of active LPF R7 0805 100 kΩ part of HPF for audio output RL0 0805 100 kΩ NIP 2.2 kΩ load for 10. 7MHz filter RP 0805 3.3 kΩ 3.3 kΩ CERDIS loading resistor XTAL HC49 SMD 10.245 MHz 20.945 MHz FIL1 FIL2 Lead type Lead type 10M15A CFWLA455KEFA 21M15A CFWLA455KEFA CERDIS SMD Lead type CDBKB455KCAY07 CDBLA455KCAY07 CDBKB455KCAY07 CDBLA455KCAY07 U1 Note: fundamental-mode crystal for 455 kHz IF2 crystal filter ceramic filter from Murata or equivalent part ceramic Discriminator from Murata or equivalent part - NIP – not in place, may be used optionally 39011 07122 01 Rev. 004 Page 16 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 7 ASK (OOK) Detectors and RSSI The logarithmic RSSI signal is used for ASK detection. When the TH7122x is switched to ASK mode, the RSSI pin 7 is internally connected to the OUT_DEM pin 6 in order to feed the RSSI signal directly to the data slicer which is setup by OA1. Therefore only one capacitor is needed to set the detector bandwidth on either pin 7 or 6. Below is a typical RSSI graph. The curves show the voltage at pin RSSI versus RF input power for both settings: LNA high and low gain. Typical RSSI curve 1.8 1.6 1.4 RSSI / V 1.2 1.0 high LNA gain low LNA gain 0.8 0.6 0.4 0.2 0.0 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 RF input / dBm Fig. 3: RSSI output voltage vs. RF input level Note the following: • • • There is a variation in the absolute value of the RSSI voltage vs RF signal level. Therefore, the absolute value for the RSSI voltage is not an accurate indication of the signal level. The slope of all the curves is relatively constant. The usable RSSI range is about 70dB When the RSSI signal is used for ASK detection, the absolute value of the voltage is not important. 39011 07122 01 Rev. 004 Page 17 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 17 FS0/SDEN FS1/LD 19 VEE_DIG 18 TNK_LO 21 LF 23 OUT_PA VCC_PLL 20 25 VEE_PLL 22 24 ASK (OOK) data detection can be done two ways: 7.1 ASK Detector - Standard 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 IN_DEM INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 IN_IFA 1 32 OUT_MIX VCC_IF RO 10 3 FSK_SW 11 31 VEE_IF 2 30 IN_MIX C3 17 FS0/SDEN 1.5nF VEE_DIG 18 FS1/LD 19 TNK_LO 21 VCC_PLL 20 LF 23 OUT_PA VEE_PLL 22 24 C5 7.2 ASK Detector - Peak Detector 16 26 IN_LNA RE/SCLK 15 27 VEE_LNA VCC_DIG 14 28 OUT_LNA ASK/FSK 13 TH7122x 29 GAIN_LNA IN_DTA 12 INT2/PDO INT1 OUT_DEM RSSI OUT_DTA 4 5 6 7 8 9 VEE_RO OUT_DTA C6 100nF 39011 07122 01 Rev. 004 100k R1 R2 680k IN_IFA 1 VCC_IF RO 10 IN_DEM 31 VEE_IF 3 FSK_SW 11 2 30 IN_MIX 32 OUT_MIX The detector bandwidth is set by the RSSI output impedance of 33kΩ and C5. OUT_DTA 10nF 25 9 VEE_RO This bit slicer is very simple. The time constant is approximately 200kΩ · C3. It works for both ASK and FSK reception. For NRZ data, the ratio of 1’s to 0’s should not be greater than about 5:1 because this method operates by filtering the average voltage of the data signal to the data comparator. If the data is RZ like Manchester, this is not a problem. C5 This circuit can be used for ASK if the DC component of the data is not constant. This is usually the case for NRZ (non-return-to-zero) codes. C6 is charged by the peak detector. The discharge time constant is C6 · (R1 + R2). Pins 6 and 7 are connected together, so one capacitor, C5 sets the detector and RSSI frequency response. R1 is selected to be 100kΩ, and then R2 is set to give the desired offset to the (-) input of the internal OA1 (the output data comparator). If the system is designed to operate at short ranges, R2 can be reduced to lower noise and interference. 1.5nF Page 18 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 8 RF Input Matching The LNA input pin IN_LNA can be considered as a parallel circuit of a capacitance Cin and a resistance Rin. Cin is relatively frequency independent and at Cin = 2pF while Rin ranges from about 600Ω at 27MHz to 200Ω at 900MHz. When designing a matching network, it should end with a series inductor. A capacitor from IN_LNA to ground may cause parasitic oscillations of the LNA at high frequencies above 1GHz. At high frequencies, an inductor in series with the input can resonate with Cin. Rin is close to the required load resistance for the TH7122x power amplifier (PA), so it can be connected to the PA output pin OUT_PA as is done in the evaluation boards. The LNA noise figure is about 2.3dB while its IIP3 is about –18dBm. During transmit, the LNA input is shunted to ground. The shunt resistance is approximately 33Ω. This is to protect the LNA input and to prevent the PA output from nonlinear distortions that could otherwise be caused by the PN junction of LNA input transistor. The shunt can be turned off by setting bit 20 of the ‘B’ word to ‘0’. 9 RF Output Matching The internal PA provides an open-collector output at pin OUT_PA. In order to provide bias to the PA, this pin is usually connected to positive supply by an inductor (LTX0). The saturation voltage of the PA output is about 0.7V. In order to avoid saturation of the output stage the peak output voltage swing should be fewer than VCC - 0.7V. The maximum available output power (TXPOWER = ‘11’) for different values of the power select resistor RPS on pin 24 is given in the data sheet. Since the open-collector output transistor can be considered as a current source, the only parameters needed to design the output matching network are the output capacitance, the peak voltage swing and the power which should be delivered to the load. The equation for the optimum load resistance is given in the data sheet. An example is given for a 3V supply and to deliver 10mW: RL = (VCC − VCESAT )2 2 ⋅ PO = (3V − 0.7V )2 2 ⋅ 10mW ≈ 260 Ω According to the output power vs. RPS curve given in the data sheet, the RPS value must be approx. 30kΩ for 434MHz and 50kΩ for 868MHz applications. The internal capacitance at OUT_PA is typically 3pF. This can be part of the PI matching network or can be tuned in a parallel tank circuit together with the inductor LTX0. If the transceiver must be designed for a wide frequency range, matching is more difficult. A wide band transformer and/or multiple stage PI network can be used. If a PI network is used, LTX0 is usually made large enough to act as an open circuit for the RF signal. 39011 07122 01 Rev. 004 Page 19 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 10 LNA Output and Mixer Input Matching The LNA output is also an open collector. Normally, it is tuned with an LC circuit and coupled to the mixer with a capacitor. However, a SAW filter can be added between the LNA output and the mixer input for better image rejection. At low frequencies, a double-tuned LC filter can also be used. When the SAW filter is placed between the LNA and mixer, the receiver sensitivity is improved slightly, but the image rejection is limited by leakage between the LNA and mixer pins. Maximum image rejection can be achieved if the SAW filter is put on the LNA input. But then the system noise figure is degraded by the loss of the filter, and an RF switch is usually required for switching between transmit and receive. Similar to the LNA input the mixer input IN_MIX can also be considered as a parallel circuit of a capacitance Cin and a resistance Rin. Again Cin is relatively frequency independent but now at Cin = 1.5pF. The mixer input resistance Rin also doesn’t vary much over frequency and is approx. Rin = 200Ω. 11 Special Considerations • • • • • antenna (load) 50 L1 12nH 12nH C3 5.1pF Fig. 4: 39011 07122 01 Rev. 004 C1 C2 2.7pF R1 100 • • VCOCUR should always be set to the lowest possible setting (‘00’) on receive. This is important at frequencies above 500MHz to prevent excessive VCO signal levels on the antenna (LO leakage). It usually gives the best receive sensitivity at frequencies below 500MHz. The high VCOCUR setting (‘11’) is usually used for transmit. The largest possible capacitor should be added in parallel with RPS when transmitting ASK signals. This reduces the rise time of the PA turn on and improves the ASK spectrum. A 1nF capacitor is used in the evaluation boards. Pin 27 is the LNA ground and the PA ground. This pin should be connected to the ground plane and a ground trace on the top layer connecting it to the output connector ground. Resistors between a microcontroller and the SCI pins 15,16,17 will reduce interference caused by the microcontroller. 10kΩ can be used on pins 15 and 16 and a larger value up to 100kΩ can be used on pin 17 because this pin does not have a 120kΩ internal resistor to ground. Always use the highest possible PLL reference frequency for transmitting ASK. It should be 200kHz or higher. For frequencies like 315MHz, a 1MHz reference frequency can be used for transmit and 100kHz for receive. The high CPCUR setting (‘1’) should be used for ASK. When operating at 868 or 915MHz into a mismatched nearby antenna or SAW filter, signal reflections may cause instability caused by coupling to the VCO which operates at the same frequency as the output signal. This can be improved by adding a 3dB/90-degree directional coupler between the TH7122x output matching network and the antenna. Such a coupler can be purchased as a thin film circuit or constructed with a few passive components as shown in Fig. 3. 2.7pF TH7122x output matching network L2 R2 50 • 3dB/90° directional coupler setup with LC components for 868/915MHz Page 20 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook • • When programming a TH7122x operating at 5V from a PC using the parallel port, the voltage output from the PC is sometimes not large enough to reach 0.7*VCC (3.5V), and the TH7122x will not program. This can be fixed by lowering VCC to 4.5V for programming or adding 10k pull-up resistors on the SCI lines or by adding a non-inverting buffer IC with open collector outputs pulled up to Vcc with resistors. The TH7122x sensitivity can be improved by adding an LNA stage before the TH7122x. In this case, a SAW filter should be placed between the LNA and IN_LNA of the TH7122x so the IM performance of the TH7122x is not degraded by the extra gain of the LNA. And, it may be necessary to put a T/R switch on the antenna to switch between transmit and receive. 12 EVB7122 Special Evaluation Board The normal EVB7122 is used for standard ASK/FSK applications at 315, 433.92, 868.3, and 915MHz. It uses a reference crystal frequency of 7.1505MHz so that the programming pins on the EVB7122 will produce the correct transmit and receive frequencies without any external programming. For other frequencies and special applications, the EVB7122-special is available. It has additional pads for applications such as: • Narrow band • High speed • External varactor • AFC with a ceramic or coil discriminator • A SAW filter between the LNA and mixer • A matching network between the mixer out and IF filter • Direct VCO modulation This board is normally supplied with an 8.000MHz reference crystal to make programming via the SCI bus easier. For example, with 25kHz channel steps, NR and NT would be set to 320. For frequency hopping applications in the 902-928MHz band 400kHz frequency steps could be used, so NT could be set to 20. Also the coil pads are 1008 size so larger values needed for low frequencies can be used. For ASK applications, setting NT to 8 gives a transmit PLL reference of 1.0MHz. This gives very good ASK results for frequencies like 315 to 434MHz or even 915 MHz where the frequency is on even 1MHz centers. In this case NR could be set to 80 to allow tuning to the 10.7MHz offset for the receiver. Several application schematics and PCB top layer arrangements are shown in figures 12.1 to 12.4. The bottom layer is almost all ground except for a Vcc trace which is placed there so it will not interfere with the text near the input and output pins. Thru-holes are used for the IF filter so wide and narrow ceramic as well as crystal filters can be used. The pads for the IF matching network are 1210 size because these are usually in the range from 2.2 to 10uH. 39011 07122 01 Rev. 004 Page 21 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook VCC GND GND SDTA SDEN SCLK IN_DTA GND OUT_DTA GND RSSI GND OUT_DEM GND 12.1 Circuit Schematic Direct VCO Modulation for Narrow Band with SAW Filter 2 1 4 3 2 1 4 3 2 1 4 3 2 1 RS1 CB0 CM2 RM2 RS3 RS2 RM3 CX1 LTX0 CTX1 CTX0 LRX2 CRX0 9 VEE_RO RO 10 FSK_SW 11 IN_DTA 12 32 OUT_MIX 31 VEE_IF 30 IN_MIX 1 IN_IFA CTX2 50 CERDIS RL0 CB4 C2 CERFIL LSF1 CSF2 LIF1 CSF1 CTX3 CB5 CIF1 CIF2 LTX1 TX_OUT RX_IN L1 6 4 1 3 SAWFIL VCC VCC CB2 29 GAIN_LNA CTX4 28 OUT_LNA OUT_PA VCC_IF 2 26 IN_LNA IN_DEM 3 23 LF 24 RPS CP RP INT2/PDO 4 22 VEE_PLL 25 VD1 RF1 C4 C3 INT1 5 TH7122 21 TNK_LO CF2 39011 07122 01 Rev. 004 ASK/FSK 13 OUT_DEM 6 20 VCC_PLL L0 C5 RSSI 7 27 VEE_LNA C0 RM1 CF1 OUT_DTA 8 18 VEE_DIG 19 FS1/LD R01 RF VCC_DIG 14 16 FS0/SDEN 17 C01 CM1 RE/SCLK 15 CB6 RB0 XTAL CB7 LD CSF3 CSF4 C1 Page 22 of 32 CB1 RB1 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 1 1 1 GND OUT DEM GND RSSI GND OUT DTA GND IN DTA SCLK SDEN SDTA GND GND VCC 12.1.1 Component Arrangement Top Side for schematic 12.1 1 C5 C4 XTAL RS3 C3 CB7 RS1 LD CM2 CM1 RM2 CB0 RM1 RS2 RM3 CX1 RB0 CP C01 L0 C0 R01 CB6 CF2 CF1 RF VD1 RP RF1 CB5 CB4 RL0 C2 LTX1 CTX3 CB1 CIF1 LSF1 CTX1 LIF1 CIF2 CSF3 CB2 CSF2 CSF1 LRX2 RB1 CTX2 RX_input TX_output Melexis EVB7122 special CSF4 C1 LTX0 39011 07122 01 Rev. 004 CERFIL L1 CRX0 CTX0 CTX4 Board size is 39.5mm x 56.5mm Page 23 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook VCC GND GND SDTA SDEN SCLK IN_DTA GND OUT_DTA GND RSSI GND OUT_DEM GND 12.2 Circuit Schematic High Speed Data Communication 2 1 4 3 2 1 4 3 2 1 4 3 2 1 RS1 CB0 RS3 RS2 CX1 XTAL 9 RL2 OUT_DTA 8 TH7122 21 TNK_LO VCC CB2 LTX0 CTX0 LRX2 CRX0 CTX1 CTX2 50 LTX1 31 VEE_IF 32 OUT_MIX 30 IN_MIX CTX4 29 GAIN_LNA 24 RPS 28 OUT_LNA VCC_IF 2 27 VEE_LNA 23 LF OUT_PA IN_DEM 3 26 IN_LNA CF2 C3 R RL1 INT2/PDO 4 22 VEE_PLL 25 CF1 INT1 5 RP CB5 1 IN_IFA CERDIS RL0 CB4 C2 CERFIL C1 L1 CB1 VCC 20 VCC_PLL RM1 RF 39011 07122 01 Rev. 004 OUT_DEM 6 19 FS1/LD L0 C5 RSSI 7 18 VEE_DIG CM1 C4 VEE_RO RO 10 IN_DTA 12 FSK_SW 11 ASK/FSK 13 RE/SCLK 15 16 FS0/SDEN 17 VCC_DIG 14 CB7 LD TX_OUT RX_IN Page 24 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 1 1 1 1 C5 C4 RL1 XTAL RS3 RS1 RL2 C3 CB7 LD CM1 RM1 RS2 RM3 CB0 GND OUT DEM GND RSSI GND OUT DTA GND IN DTA SCLK SDEN SDTA GND GND VCC 12.2.1 Component Arrangement Top Side for schematic 12.2 CX1 RB0 CB6 L0 CF2 CF1 RF RP CB5 CB4 RL0 C2 CERFIL C1 CB2 LTX0 CB1 L1 CRX0 CTX0 CTX4 LTX1 EVB7122 special CTX1 0 CTX2 RX_input TX_output Melexis 39011 07122 01 Rev. 004 LRX2 Board size is 39.5mm x 56.5mm Page 25 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 4 3 2 1 RS1 CB0 GND GND SDTA SDEN SCLK 2 1 IN_DTA GND VCC GND 12.3 Circuit Schematic 433MHz - NB - 10.7MHz ext. IF 4 3 2 1 RS3 RS2 CX1 LD 9 RO 10 IN_DTA 12 FS0/SDEN 17 FSK_SW 11 CB6 ASK/FSK 13 CM1 RE/SCLK 15 RB0 VCC_DIG 14 16 CB7 OUT_DTA 8 RSSI 7 18 VEE_DIG OUT_DEM 6 19 FS1/LD 20 VCC_PLL 21 TNK_LO CTX4 CB2 LTX0 CTX1 CTX0 LRX2 CRX0 32 OUT_MIX 24 RPS 31 VEE_IF VCC_IF 2 30 IN_MIX 23 LF OUT_PA IN_DEM 3 26 IN_LNA RF INT2/PDO 4 22 VEE_PLL 25 CF2 VD1 RF1 INT1 5 TH7122 29 GAIN_LNA L0 28 OUT_LNA C01 RM1 27 VEE_LNA CF1 VEE_RO XTAL CB5 1 IN_IFA C2 see Fig.2 IF_IN CTX2 50 LTX1 L1 TX_OUT RX_IN C1 RB1 CB1 VCC VCC (10.7MHz) CTX3 Software Settings: Reference oscillator frequency: 8.00MHz RR = RT = 320 for 25kHz channels NR = 16 932, NT = 17 360 VCOCUR = ‘11’ 39011 07122 01 Rev. 004 Page 26 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 4 3 2 1 RS1 CB0 CM2 RM2 GND GND SDTA SDEN SCLK 2 1 IN_DTA GND VCC GND 12.4 Circuit Schematic 868MHz - NB - 21.4MHz ext. IF 4 3 2 1 RS3 RM3 RS2 CX1 LD 9 RO 10 IN_DTA 12 FSK_SW 11 ASK/FSK 13 FS0/SDEN 17 RE/SCLK 15 CB6 RB0 VCC_DIG 14 16 CB7 OUT_DTA 8 RSSI 7 18 VEE_DIG OUT_DEM 6 19 FS1/LD 20 VCC_PLL 21 TNK_LO CB2 LTX0 CTX1 CTX0 LRX2 CRX0 32 OUT_MIX 31 VEE_IF CTX4 30 IN_MIX VCC_IF 2 OUT_PA 23 LF 24 RPS CF2 IN_DEM 3 26 IN_LNA CF1 INT2/PDO 4 22 VEE_PLL 25 RF INT1 5 TH7122 29 GAIN_LNA L0 RM1 28 OUT_LNA C01 27 VEE_LNA CM1 VEE_RO XTAL CB5 1 IN_IFA C2 see Fig.2 IF_IN CTX2 50 LTX1 L1 TX_OUT RX_IN C1 RB1 CB1 VCC VCC (21.4MHz) CTX3 Software Settings: Reference oscillator frequency: 8.00MHz RR = RT = 320 for 25kHz channels NR = 33876, NT = 34732 VCOCUR = ‘11’ Band: ‘1’ 39011 07122 01 Rev. 004 Page 27 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 13 Overview Component List for Special Boards Part Size Value Tol. C0 0805 0.5 - 3.3 pF ±5% VCO tank capacitor-to reduce VCO sensitivity Description C01 0805 7 pF - 1 nF ±5% VCO tank capacitor-sets ext varactor tuning range C1 0805 * ±5% LNA output tank capacitor-if SAW filter not used C2 0805 0.5 - 12 pF ±5% MIX input matching capacitor-if SAW filter is not used C3 0805 10 nF ±10% data slicer capacitor C4 0805 330 pF ±5% demodulator output low-pass capacitor, depending on data rate C5 0805 1.0 nF ±10% RSSI output low pass capacitor CB0 0805 10 µF ±20% de-coupling capacitor CB1 0805 330 pF - 10 nF ±10% de-coupling capacitor-depends on frequency CB2 0805 330 pF - 10 nF ±10% de-coupling capacitor-depends on frequency CB4 0805 10 nF ±10% de-coupling capacitor CB5 0805 100 nF ±10% de-coupling capacitor CB6 0805 100 pF ±10% de-coupling capacitor CB7 0805 100 nF ±10% de-coupling capacitor CF1 0805 1uF ±10% loop filter capacitor-for most applications CF2 0805 100 - 220 nF ±5% loop filter capacitor-for most applications CIF1 0805 27 - 68 pF ±5% filter matching capacitor-part of filter matching network CIF2 0805 68 - 100 pF ±5% filter matchingcapacitor-part of filter matching network CP 0805 0 - 12 pF ±5% CERRES tuning capacitor-not needed with CDSCB10M7GA136 CRX0 0805 100 pF - 10 nF ±5% RX coupling capacitor-depends on frequency CSF1 0805 * ±5% capacitor to match SAW filter output to mixer CSF2 0805 * ±5% capacitor to match SAW filter output to mixer CSF3 0805 * ±5% capacitor to match SAW filter input-capacitive divider on L1 CSF4 0805 * ±5% capacitor to match SAW filter input-capacitive divider on L1 CTX0 0805 100 pF - 10 nF ±5% TX coupling capacitor-depends on frequency CTX1 0805 * ±5% TX impedance matching capacitor CTX2 0805 * ±5% TX impedance matching capacitor CTX3 0805 * ±5% can be used to reduce 2 harmonic nd CTX4 0805 * ±5% tunes LTX0 with output C of PA CX1 0805 * ±5% Sets center frequency for ASK and NB with VCO modulation CX2 0805 * ±5% Can be used for FSK and 2 point NB modulation R01 0805 22 Ω ±5% Prevents parasitic oscillation when L0 is large for low frequencies RB0 0805 100 Ω ±5% VCO decoupling RB1 0805 100 Ω ±5% LNA decoupling from IF signals RF 0805 * ±5% loop filter resistor RF1 0805 10 kΩ ±5% varactor bias resistor RL0 0805 * ±5% RM1 0805 1 MΩ ±5% Optional CERFIL loading in parallel with 2 kΩ of IF input modulation resistor-forms voltage divider with RF RM2 0805 * ±5% modulation resistor-sets modulation sensitivity RM3 0805 10 kΩ ±5% modulation resistor RP 0805 5.6 kΩ ±5% CERDIS loading resistor RPS 0805 15k - 47 kΩ ±5% power-select resistor-sets maximum power LIF1 1210 4.7 - 10 µH ±5% filter matching inductor for NB filters RS1...RS3 0805 10 kΩ ±5% protection resistor and for filtering digital noise from micro L1 1008 * ±5% LNA output tank inductor LSF1 1008 * ±5% SAW filter matching inductor with CSF1 and CSF2 39011 07122 01 Rev. 004 Page 28 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook LRX2 1008 * ±5% LTX0 1008 * ±5% LTX1 1008 * ±5% VD1 SOD-323 XTAL HC49 SMD CERFIL CERDIS SAWFIL Note: SMD 7x3 Lead type SMD 4.5x2 SMD 3x3 * 7.1505 MHz (or 8.0000 MHz) ±20ppm cal., ±20ppm temp. SFECF10M7HA00 @ B3dB = 180 kHz SFKLA10M7NL00 @ BIF2 = 30 kHz CDSCB10M7GA136 * impedance matching inductor VCO varactor diode fundamental-mode crystal, Cload = 10 pF to 15 pF, C0, max = 7 pF, Rm, max = 70 Ω ceramic filter from Murata or equivalent part ceramic Discriminator from Murata or equivalent part low-loss SAW filter from Murata, or equivalent part * Value is determined by special application 39011 07122 01 Rev. 004 Page 29 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook 14 Special Board Layouts Board layout data in Gerber format is available board size is 56.5mm x 39.5mm. VCC EVB7122 special GND GND SDTA LD SDEN SCLK IN DTA GND Melexis OUT DTA GND RSSI GND OUT DEM GND PCB top view PCB bottom view 39011 07122 01 Rev. 004 Page 30 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook Your Notes 39011 07122 01 Rev. 004 Page 31 of 32 AN7122x-Cookbook Dec./05 Application Note Transceiver TH7122x Cookbook Your Notes For the latest version of this document. Go to our website at www.melexis.com Or for additional information contact Melexis Direct: Europe and Japan: All other locations: Phone: +32 1367 0495 E-mail: [email protected] Phone: +1 603 223 2362 E-mail: [email protected] ISO/TS16949 and ISO14001 Certified 39011 07122 01 Rev. 004 Page 32 of 32 AN7122x-Cookbook Dec./05