TRF6901_08 Datasheet, PDF (11/32 Pages) Texas Instruments – SINGLE-CHIP RF TRANSCEIVER

TRF6901
SINGLEĆCHIP RF TRANSCEIVER
SLWS110G − SEPTEMBER 2001 − REVISED JUNE 2004
detailed description (continued)
demodulator
The quadrature demodulator decodes digital frequency shift keying (FSK) modulation. An external ceramic
discriminator or an equivalent discrete circuit is required at terminal 35. The demodulator is optimized for use
with a ceramic discriminator. Thus, the use of a packaged ceramic discriminator is recommended for the best
performance. Internal resistors can be programmed with D<14:12> to tune the demodulator center frequency.
The recommended default setting for the demodulator tuning bits is D<14:12> = 110. The resonant frequency
of the discrete-component discriminator can be calculated from the inductor and capacitor values used in the
circuit. A parallel resistor may be added to reduce the quality factor (Q) of the tank circuit, depending on the
application.
ƒ_res
+
2p
1
Ǹ_LC
External Tank
35
L
R
C
Figure 4. Optional External Discrete Demodulator Tank
post-detection amplifier/low-pass filter
The post-detection amplifier operates as a low-pass transimpedance amplifier. The external low-pass filter
circuit must be optimized for the data rate. The 3-dB corner frequency of the low-pass filter should be greater
than twice the data rate. Various low-pass filter designs use two to five components and may be first- or
second-order designs. Simple 2-element filter component values and 3-dB bandwidths are contained in Table 1.
R2
External
Low-Pass
Filter
C2
37
36
C1
R1
Internal Low-Pass Amplifier
Figure 5. Post-Detection Amplifier/Low-Pass Filter
Table 1. Various Post-Detection Amplifier/Low-Pass Filter
3-dB Bandwidth and Corresponding Component Values
f3dB (kHz)
10
20
30
60
R2 (kΩ)
220
220
220
220
C2 (pF)
68
33
22
10
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