BC2401 Application Guidelines
LNA
VCO
Quench
Signal
generator
Digit
Demodulator
HIRC
RFIN
L1
L2
DOUT
VDDRF
VSSRF
VDD VSS
BC2401 Application Guidelines
D/N: AN0435E
Introduction
Holtek’s BC2401 is an RF receiver which supports OOK demodulation in the 315MHz and
433.92MHz frequency bands. The device includes fully integrated super regeneration
signal reception technology to achieve the best performance/cost ratio. For product
development convenience, the BC2401 can detect received signals by reading the pin
state directly. The BC2401 can operates with a simple OOK modulation RF transmitter to
develop wireless products, such as wireless transmission controls for home appliances,
computer peripherals and radio controlled toys to name but a few.
As mentioned above, the BC2401 is an RF receiver. Product design engineers, when
using such products for the first time, are often faced with some difficult problems during
product design. Holtek has prepared solutions including some frequently asked questions
based on their past experience to help engineers to quickly understand the RF receiver
operation to overcome these initial problems. This application note will show how to use
the BC2401 using specific examples.
Functional Description
The BC2401 is a super regeneration architecture RF receiver which contains a front-end
receiver and a digital demodulator. The architecture is shown as follows.
The reception signal frequency can be setup by external reactive components connected
to L1 and L2. The internal oscillator will operate continuously after power-on to provide
frequency for the demodulator. When the signal frequency has been setup by the
AN0435E V1.00 1/ 8 December 11, 2016
components on L1 and L2, the relevant output signal will be generated on the DOUT pin
once the device is powered on.
Feature
Decoder IC
BC2401 AntennaData Out Match Circuit
BC2401 Application Guidelines
The above figure shows the general design architecture of the BC2401. An antenna, a
matching circuit, a BC2401 device and a decoder IC are all that is necessary to
implement a high frequency signal receiver function.
The BC2401 contains the following features:
Supports RF OOK ASK demodulation
Operating voltage: 4.0V~5.5V
Operating bandwidth: 300MHz~450MHz
Symbol rate: 5Kbps
High sensitivity: -100dBm@5V / 0.1%BER / 315MHz / 433MHz
Operating current consumption less than 4mA
Integrated LNA and super regeneration oscillator
Small package type: 8-pin SOP
Application Circuits
Note: Special attention should be paid to three parts in the circuit. The first part is the
antenna part labeled with ANT1, the second part is the high frequency input matching
circuit which includes C5 and L2 while the third part is the LC Tank circuit which contains
L1, C6 and L3. More detail information will be introduced in the following sections.
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BC2401 Application Guidelines
Value
315MHz
433MHz
U1
BC2401
—
Pcs
Holtek
BC2401
R1
Resistor
1k
Ω
Walsin
WR06X102JRR
C1
Capacitor
10μ
F
muRata
GRM188B30J106ME47#
C2
Capacitor
0.1μ
F
muRata
GRM188R71H104KA93#
C3
Capacitor
0.1μ
F
muRata
GRM188R71H104KA93#
C5
Capacitor
3.5p
2p F muRata
GQM1875C2ExRxCB12#
C6
Capacitor
5.5p
3p F muRata
GQM1875C2ExRxCB12#
L1
Inductor
39n
H
ACX
HI0603-1B39N_H_
L2
Inductor
39n
27n H ACX
HI0603-1BxxN_H_
L3
Adjustable inductor
3.5
T
GANG SONG
MD-0507U-3.5T-S-BR
63
2
1
)(
C
L
f
Frequencyπ=
6
2
3
)2(
1
Cf
L
π
=
3
2
6
)2(
1
Lf
C
π
=
OSC 2
OSC 1
C 6
L 3
L 1
Bill of Materials:
Symbol Description
LC Tank Selection Guides
The BC2401 reception frequency is setup by inductors and capacitor connected between
Pins 7 and Pin 6, as shown below.
The relationship between the inductor, capacitor and the frequency setup is shown as
follows.
Unit Vendor Part Number
Users should initially decide upon their desired reception frequency before choosing the
component values. After determining the frequency, then choose the actual value of
either the inductor or the capacitor, after which the other component values can be
calculated using the following equations:
Condition 1: If the frequency and capacitance have been determined:
Condition 2: If the frequency and inductance have been determined:
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BC2401 Application Guidelines
315MHz
433MHz
L1
39nH
C6
5.5pF
3pF
L3
3.5T
3.5T
315MHz
433MHz
C5
3.5pF
2pF
L2
39nH
27nH
Antenna
C 5
L 2
R FIN
It is recommended that low tolerance inductor and capacitor should be used to effectively
improve the reception sensitivity. Recommended values for the different frequency bands
are shown in the following table.
Note: The adjustable inductor L3 should be finely tuned.
RF Input Matching Circuit Guides
To receive the radio signals, as well as requiring an antenna, an impedance matching
circuit is also required as shown in the following figure. Good impedance matching can
reduce noise thus improving reception sensitivity. A network analyzer will normally be
required to adjust the impedance matching. The selected capacitor and inductor should
have high Q values for improved reception sensitivity.
The recommended values for the different frequency bands for the PCB Layout are listed
in the following table.
Note: If the PCB layout is changed, the impedance matching circuit should be adjusted
accordingly.
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BC2401 Application Guidelines
Antenna Selection Guides
Users can select a dipole or patch antennas with a 50Ω SMA interface as shown in the
following diagram.
Or use a λ/4-long copper wire, single conductor or stranded wire, shown as follows.
Attention should be paid to the considerations in the next section for laying out an
antenna directly on the circuit board.
PCB Layout Note
Component Placement Rules
The first consideration should be RF signal path. The RF-related components placement
and the PADs between these components should be placed as close as possible to the
device to minimise the wire length.
Enough space must be reserved for the extra width of the VCC and GND traces.
Routing
As right angle routing tracks accumulate charges more readily and may affect PCB
stability it is better to use 45 degree bevel or arc angles as far as possible when routing.
The distance between two traces should not be less than 6 mils.
The distance between a trace and through holes should not be less than 6 mils.
The distance between two adjacent through holes should not be less than 6 mils.
The width of the VCC and GND main traces should not be less than 12mils.
Power lines should be connected to a bypass capacitor located near the IC power pins.
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BC2401 Application Guidelines
Antenna
The bottom layer beneath the RF antenna components should not have poured copper
traces to avoid adversely affecting the RF performance.
The RF matching components should have poured copper traces to increase stability.
With the exception of RF matched components, other components should not be located
near the antenna to reduce interference on the RF circuits.
PCB Layout Example
Top View
Bottom View
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BC2401 Application Guidelines
Conclusion
This application note has introduced how to use the Holtek BC2401 device, a super
regeneration high frequency receiver, in which a matching circuit is required to be
connected to the high frequency input pin, RFIN, and how an adjustable inductor is
adjusted according to the desired frequency band.
Version and Modification Information
Date Author Issue
Reference Files
Reference file: BC2401 Datasheet.
For more information, refer to the Holtek official website http://www.holtek.com.tw/home.
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2016.07.7
何信智(Ho,Walers)
First Version
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BC2401 Application Guidelines
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AN0435E V1.00 8/ 8 December 11, 2016
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