Can I use the Si4x6x and Si4x5x radio chips without the matching balun on the RX side? What are the sensitivity numbers in that case?
The Si4x6x and Si4x5x radio chips can be used without the use of the 4-element discrete matching balun transformator. In this case only two bypass capacitors are required at the RX pins and in this way an ultra low-cost all-band RX solution can be got. The basic idea is to use the originally differential receiver as a simple single-ended one. For this, one of the RX pins should be connected to ground - via a bypass capacitor - and the other RX pin should be used as a single-ended input.
Here is the schematic sketch of the forced single-ended receiver:
Of course, the sensitivity will be slightly degraded compared to the case when the balun matching network is applied. Here are some sensitivity numbers in case of using this ultra low-cost single-ended solution:
315 MHz: -101.4 dBm
434 MHz: -101.1 dBm
868 MHz: -99.5 dBm
915 MHz: -99.1 dBm
With the following conditions:
2-GFSK modulation, 100 kbps data rate, 50 kHz frequency deviation, RxBW is approx. 200 kHz, BER < 1e-3.
Measured on the 4362-PRXBxxx reference Pico Board (WES0002, LR1: not mounted, CR1: bypass capacitor, LR2: not mounted, CR2: bypass capacitor, CC: zero ohm).
So, basically the sensitivity is approximately -101 dBm at the low frequency bands and -99 dBm at high-bands. These numbers are about 1-1.5 dB worse in case of using Si4x5x radio chips.
Some additional notes:
- this solution can be applied where the RX side is not directly connected to the TX path (i.e. this solution cannot be used in Direct-tie configuration)
- at higher-Z termination (300-500 ohm) the sensitivity can be improved (see AN643 for the optimum terminations)
What kind of RF-switch is recommended for the replacement of the uPG2214 SPDT RF-switch used in most of the Si4x6x-based reference designs?
The RF-switches listed below can be good alternatives to replace the uPG2214 SPDT RF-switch. These switches have approximately the same specifications/characteristics/ratings and footprint as the uPG2214.
Example list of RF switches for the replacement:
- CG2179M2: http://www.cel.com/pdf/datasheets/CG2179M2.pdf
- AS213-92: http://www.skyworksinc.com/Product/57/AS213-92LF
The RF switch used in the designs needs to have:
- low insertion loss
- high enough frequency capability
- high isolation
- high enough power capability
- low harmonic re-generation, i.e. low distortion
- small size
Good references for RF switch IC selection guide:
Why are Si41xx-BM and Si41xx-BT devices unavailable for order?
Per Process Change Notice #0501071 dated effective 07JAN05, the lead finish version RF Synthesizers were replaced by lead free versions. So for example, P/Ns Si4133-BM and Si4133-BT were replaced by Si4133-D-GM and Si4133-D-GT.
Why is the Si4133W unavailable for order?
The Si4133W RF Synthesizer, i.e. the wide temperature operation version of the Si4133, was sold as a product line by Silicon Labs to NXP as part of the Aerophone technology sale in 2007. NXP then briefly sold it as the Aero4133, discontinuing it at the end of 2008.
What are the exact XTAL specification requirements for Si443x radio?
- C_load: 8...12pF
- ESR <= 50ohm
- C0 < 5pF
Further details on the Si443x family crystal oscillator can found in AN417 Application Note.