Texas Instruments TMS3637P, Data Manual

Page: 42 / 53

6–10
6.5 Radio Frequency (RF) Coupling of Transmitter and Receiver
Table 6–6 lists the parts for the schematic of a radio frequency transmitter and receiver shown in Figure 6–7.
In Figure 6–7, the transmitter is configured as a normal continuous transmitter and the content of the
configuration of the EEPROM cells is:
CA CB CC CD CE CF CG CH CI
1 1 1 0 0 0 0 0 0
The oscillating frequency of the transmitter is about 5.7 kHz, and the transmitter code is pulse modulated.
Table 6–6. RF Transmitter Component Functions
DEVICE FUNCTION
U1 TMC3637 configured as a transmitter
R1 Resistor on OSCR that, in conjunction with C1, determines the internal oscillator frequency of U1.
R2 Base drive current-Limiting resistor for Q1
C1 Capacitor on OSCC that, in conjunction with R1, determines the internal oscillator frequency of U1.
C2 Capacitive part of LC tank circuit variable for frequency adjustment (2 pF – 10 pF)
C3 Power-supply bypass capacitor (to present low impedance to RF on VCC)
L1 Inductive part of LC tank circuit-strip-line type
L2 RF choke presents high impedance to RF between the tank and VCC.
Q1 The npn RF transistor turns on the LC circuit.
R1
22 k
Ω
OSCR OSCC TIME GND
VCC IN CEX OUT
U1 (transmitter)
R2
15 k
Ω
VCC
C3
10 pF
Q1
L2
10
µ
H
L1
C2
10 pF
C4
2.2 pF
S1
C1
100 pF
8 7 6 5
1 2 3 4
Figure 6–7. Radio Frequency Transmitter
Inductance L2 is an RF choke, while L1 is a strip-line 0.1-
µ
H inductance that is 1.5-mm wide and 3.5-cm
long. The frequency range of the transmitter (tunable by C2–10 pF) is approximately 165 MHz – 370 MHz.
A good RF transistor with an H
FE
exceeding 500 MHz is recommended. No external antenna is required,
provided the recommended antenna is used on the receiver as described in the following paragraphs.