LMX25714 FSK Modulation in SPI Mode - Technical Information and Setup Description

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Explore the LMX25714 FSK modulation setup using SPI mode, including specifications, limitations, SPI examples, and results. Learn about the pattern generator, Gaussian transmission, symbol oversampling, frequency deviation, and key advantages of the system. Discover new improvements in the upcoming silicon and the self-calibrated system operation. View related images and PCB details from September 2014.

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LMX2571 4 FSK modulation in SPI mode. TI Information Selective Disclosure TI Confidential Maximum Restrictions

Setup description A pattern generator is streaming SPI write to produce the 4 FSK modulation. 160 random symbol are being sent in a loop so randomization is not ideal. Specifications: Gaussian transmission 4FSK BT = 0.63 Symbol oversampling = 4 Symbol rate = 60kHz Fc = 868 MHz Freq. deviation +/- 17 and +/- 50 kHz. Limitations: Current silicon requires 2 SPI write per data point Current setup (wirering/pcb) does not allow speed to go to 110k symbol/s. New Si will: have I2S style interface and SPI specifications is 50 MHz now 2 TI Confidential Maximum Restrictions

SPI example R11 and R37 are written for each data point. Each register is 24 bit long and includes address (8 bit) and data (16 bit): time[us] 0.000000 2.272727 4.545455 freq[kHz] 49.9 49.9 49.1 code R11 [hex] 0B003E 0B003E 0B003D code R37 [hex] 0252C38 0252C38 0252C38 Key advantages of this technique are: Self calibrated system with closed loop operation. Immune from process, voltage and temperature. No additional components required. 3 TI Confidential Maximum Restrictions