CC1070_12 Datasheet, PDF (13/57 Pages) Texas Instruments – Single Chip Low Power RF Transmitter for Narrowband Systems

CC1070
6 Circuit Description
RF_OUT
:2
:2
FREQ
SYNTH
Power
Control
Multiplexer
BIAS
XOSC
R_BIAS
XOSC_Q1 XOSC_Q2 VC CHP_OUT
Figure 2. CC1070 simplified block diagram
DIGITAL
INTERFACE
TO µC
DIGITAL
MODULATOR
- Modulation
- Data shaping
- Power Control
LOCK
DI
DCLK
PDO
PDI
PCLK
PSEL
A simplified block diagram of CC1070 is
shown in Figure 2. Only signal pins are
shown.
During transmit operation, the synthesized
RF frequency is fed directly to the power
amplifier (PA). The RF output is frequency
shift keyed (FSK) by the digital bit stream
that is fed to the DI pin. Optionally, the
internal Gaussian filter can be enabled for
Gaussian FSK (GFSK).
The frequency synthesizer includes a
completely on-chip LC VCO. The VCO
operates in the frequency range 1.608-
1.880 GHz. The CHP_OUT pin is the
charge pump output and VC is the control
node of the on-chip VCO. The external
loop filter is placed between these pins. A
crystal is to be connected between
XOSC_Q1 and XOSC_Q2. A lock signal is
available from the PLL.
The 4-wire SPI serial interface is used for
configuration.
7 Application Circuit
Very few external components are
required for the operation of CC1070. A
typical application circuit is shown in
Figure 3. The external components are
described in Table 9 and values are given
in Table 10.
Output matching
L2, C2 and C3 are used to match the
transmitter to 50 Ω. See section 13 on
page 26 for details. Component values for
the matching network are easily calculated
using the SmartRF^® Studio software.
Bias resistor
The precision bias resistor R1 is used to
set an accurate bias current.
PLL loop filter
The loop filter consists of two resistors (R2
and R3) and three capacitors (C6-C8). C7
and C8 may be omitted in applications
where high loop bandwidth is desired. The
values shown in Table 10 can be used for
data rates up to 4.8 kBaud. Component
values for higher data rates are easily
found using the SmartRF^® Studio
software.
Crystal
An external crystal with two loading
capacitors (C4 and C5) is used for the
crystal oscillator. See section 17 on page
34 for details.
Additional filtering
Additional external components (e.g. RF
LC or SAW filter) may be used in order to
improve the performance in specific
applications. See section 13 on page 26
for further information.
Power supply decoupling and filtering
Power supply decoupling and filtering
must be used (not shown in the
application circuit). The placement and
size of the decoupling capacitors and the
power supply filtering are very important to
SWRS043A
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