Datasheet
C
LPF
PGA
PA
1
2 f 22 kp W´ ´ ´
C =
See Note 3
Tx_F_OUT
Tx_PGA_
IN
PA_OUT1
PA_OUT2
Tx_PGA_
OUT
PA_IN
C
C
Inside the AFE030
510 W 510 W
See Note 2
MCU
Tx_F_IN1
Tx_F_IN2
GPIO
GPIO
See Note 1
43 kW
43 kW
AFE030
SBOS588A –DECEMBER 2011– REVISED DECEMBER 2011
www.ti.com
(1) When using both Tx Filter inputs, use 43-kΩ resistors to match the input resistance for best frequency response.
(2) Refer to Table 2.
(3) For capacitor value C, f is the desired lower cutoff frequency and 22 kΩ is the PA input resistance.
Figure 31. Recommended Tx Signal Chain Connections in PWM Mode
Using Two PWM Signals and Additional RC Filters
For the capacitors listed in Table 2, it is recommended that these components be rated to withstand the full AV
DD
power-supply voltage.
Table 2. Recommended External R and C Values to Increase Tx Filter Response Order in PWM
Applications
FREQUENCY BAND R (Ω) C (nF)
SFSK: 63 kHz, 74 kHz 510 2.7
CENELEC A 510 1.5
CENELEC B, C, D 510 1
The Tx PGA and Tx Filter each have the inputs and outputs externally available in order to provide maximum
system design flexibility. Care should be taken when laying out the PCB traces from the inputs or outputs to
avoid excessive capacitive loading. Keeping the PCB capacitance from the inputs to ground, or from the outputs
to ground, less than 100 pF is recommended.
Rx Block
The Rx block consists of Rx PGA1, the Rx Filter, and Rx PGA2. Both Rx PGA1 and Rx PGA2 are
high-performance programmable gain amplifiers. Rx PGA1 can be configured through the SPI to operate as
either an attenuator or in gain. The gain steps of the Rx PGA1 are 0.25 V/V, 0.5 V/V, 1 V/V, and 2 V/V. The gain
steps of the Rx PGA2 are 1 V/V, 4 V/V, 16 V/V, and 64 V/V. Configuring the Rx PGA1 as an attenuator (at gains
less than 1 V/V) is useful for applications where the presence of large interference signals are present within the
signal band. Attenuating the large interference allows these signals to pass through the analog Rx signal chain
without causing an overload; the interference signal can then be processed and removed within the
microprocessor as necessary.
26 Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): AFE030