Frequency shift keying (FSK) is the modulation cornerstone of a number of digital data transmission systems. The transmit signal is fairly easy to generate, AN67391 discuss the implementation in detail. Receive processing is tolerant of a wide range of signals and relatively immune to a large class of interfering signals.
This Application Note outlines a simple, almost all-hardware method for detecting FSK signals using the analog signal processing capabilities of the PSoC 1 device. It describes circuits and signal processing techniques for demodulation. This signal processing technique is readily applicable to caller ID and several modem standards but it is not a complete modem; it does not include the phone line or other interfaces; it also does not include the data processing code.
A separate project is included and outlined in the Appendix A to simplify testing of the demodulator.
In order to be able to understand the implementation, following pre-readings are suggested:
AN2041: Understanding switched capacitor blocks – Explains the operation of switched capacitor blocks, and provides practical examples for their use.
AN2168: Understanding switched capacitor filters - Discusses how low pass, band pass and notch filters can be implemented using switched capacitor blocks.
KB Article: Implementation of a full wave rectifier and low pass filtering using all hardware technique.
Example Project |
Supported H/W and S/W |
Supported PSoC1 Devices |
|
PSoC Designer Version |
H/W Kit |
CY8C20xxx |
CY8C21xxx |
CY8C22xxx |
CY8C23xxx |
CY8C24xxx |
CY8C27xxx |
CY8C28xxx |
CY8C29xxx |
|
Yes |
5.1 |
CY3210-PSoCEVAL1 |
|
|
|
|
|
x43 |
x |
x66 |
|