TDA5230 Datasheet, PDF (73/186 Pages) Infineon Technologies AG – Universal Low Power ASK/FSK Single Conversion Multi-Channel Image-Reject Receiver

TDA523x
Functional Description
Accuracy is optimized by trimming true RSSI at noise level (no input signal) to a
calculated value of -0.92 to 0.90 and at strong input signals (about -10 dBm) to +1.
It is recommended either to use RSSI with the default settings (minimum offset, minimum
gain) or to use the following trim procedure. This guarantees optimal ASK sensitivity. It
is not recommended to use trimming to increase RSSI resolution or slope.
Recommended Analog Trimming Procedure:
• Download configuration file
• Send 0x35 to the register LIMC1; this enables the RSSI buffer, selects RSSI-, and
sets the RSSI offset to a middle value
• Measure RSSI- voltage at RSSI pin (26)
• Send 0x55 to the register LIMC1, REF+ is selected
• Measure REF+ voltage at RSSI pin (26)
• Send 0x75 to the register LIMC1, REF- is selected
• Measure REF- voltage at RSSI pin (26)
• Send 0x15 to the register LIMC1, RSSI+ is selected
• Measure a RSSI voltage curve at RSSI pin (26) from noise or (no input signal) to a
high signal (about -10 dBm) using a continuous wave input signal.
• Normalize the curve using the formula for true RSSI earlier in this chapter
• Change LIMOFFS (LIMC1, bit 0..3) until true RSSI without input signal is between -
0.92 and -0.9
• Change LIMGAIN (LIMC0, bit 0..4) until true RSSI at -10 dBm is smaller but next to
+1
• The new values for LIMGAIN and LIMOFFS must be added to the configuration!
See also the Recommended Digital Trimming Procedure in Chapter 2.4.8.3 RSSI Peak
Detector. If trimming is required it is only necessary to do either analog or digital
trimming, but results of the two trimming procedures are slightly different.
Usually, it is recommended to use the digital RSSI.
Recommended applications for the analog RSSI are:
• Debugging and watching RF traffic
• External ASK demodulation
• Relative signal power measurements
If optimal accuracy is required and to reduce thermal drift, it is recommended to read all
four RSSI signals (RSSI+, RSSI-, REF+ and REF-) within a few seconds.
Data Sheet
69
Version 4.0, 2007-06-01