PART AN95021
433MHz front-end with the SA601 or
SA620
author 1995 Mar 3
INTEGRATED CIRCUITS
Philips Semiconductors Application note
AN95021433MHz front-end with the SA601 or SA620
Author: Rob Bouwer
4–2
1995 Mar 3
ABSTRACT
Although designed for 1GHz, the SA601 and SA620 can also be
used in the 433MHz ISM band. The SA601 performs amplification
of the antenna signal and down conversion to a first IF. The SA620
has the same functionality, but also has a VCO on-chip. This VCO
drives the mixer, so no external LO signal is required.
Applying the SA601 or SA620 means that a receiver with high
sensitivity and wide dynamic range can be built without a lot of
external components. The design will be easier compared with
discrete Front Ends.
Combined with an IF system like the SA676, a high performance
dual conversion receiver can be built. This receiver can operate
from 2.7 to 5.5V allowing the use of a 3-cell battery. IF frequencies
can be chosen according to one’s needs with a maximum first IF of
100MHz and a maximum second IF frequency of 2MHz.
This application note explains how to use the SA601 or SA620 at
433MHz. The performance at 433MHz is discussed. The application
circuit diagrams that are used to obtain the measurement results are
shown.
CONTENTS
1. INTRODUCTION 4–2. . . . . . . . . . . . . . . . . . . . .
2. SA601 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Application circuit 4–3. . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Measurement results 4–4. . . . . . . . . . . . . . . . . . . . . .
2.2.1 Conversion gain, Noise Figure and IP3 4–4. .
2.2.2 Isolation 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. SA620 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Application circuit 4–4. . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Measurement results 4–6. . . . . . . . . . . . . . . . . . . . . .
3.2.1 Conversion gain, Noise Figure and IP3 4–6. .
3.2.2 Isolation 4–6. . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. CONCLUSION 4–6. . . . . . . . . . . . . . . . . . . . . . .
1. INTRODUCTION
The SA601 and SA620 address high performance applications at
1GHz like cellular and cordless phones. The SA601 comprises a
Low Noise Amplifier (LNA) and a Mixer. The SA620 comprises,
besides an LNA and Mixer, a VCO (V oltage Controlled Oscillator).
Although intended for 1GHz, it is possible to apply these Front-Ends
at lower frequencies.
This paper describes the performance of these devices at 433MHz.
This band is being used for remote control systems, car alarms,
telemetry, wireless audio links, etc.
By using the SA601 or SA620 followed by, for example an SA676
FM IF, a low voltage, high performance receiver for FM, AM, FSK,
ASK demodulation can be built. The Front-Ends require only a few
passive components for decoupling and signal handling. No extra
circuitry is required for compensation for temperature and power
supply variations. This will ease your 433MHz receiver design
without trading of f performance, and give you fast time to market.
2. SA601
The SA601 comprises a 1.2GHz LNA and Mixer. The block diagram
is shown in Figure 1. In a receiver it performs the amplification of
the antenna signal and the down conversion to the first IF frequency.
This signal can then be handled by an IF system like the SA676
which takes care of AM and FM demodulation.
43215
20 19 18 17 16
761098
15 14 13 12 11
GNDMIXER
PWRDN LO IN1 LO IN2
VCC GND MIXER
IN GND MIXER
OUT GND
LNA
LO
RF IF
GND LNA IN GND
IF
GND LNA
OUT
GNDGND
MIXER
OUT VCC
VCC
BUFFER
Figure 1. SA601 Block Diagram
Using the SA601 at 433MHz will show the following differences
compared to the performance at 900MHz:
•The LNA will show a higher gain while having the same Noise
Figure (NF)
•Because of this higher gain, the Intercept point (IP3) becomes
less
The higher gain increases the sensitivity of the receiver. It also
offers the possibility to allow some mismatch at the LNA input and
hence, some gain loss. This means that a 50Ω source can be
connected directly to the LNA input without matching. In case you
do want to calculate the matching circuits for the LNA and mixer
input, Table 1 shows the S-parameters of the LNA and mixer input at
433MHz.
The IP3 performance of the SA601 at 433MHz is worse than at
1GHz. However, it is still more than sufficient for applications in the
433MHz band.
Table 1. SA601 and SA620 S-parameters
LNA Mixer
S11 S22 S21 S12 S11
R + j X R + j X R + j X
433MHz 34.0Ω - 62.8Ω55.1Ω - 47.4Ω5.4U ∠ 128°62mU ∠ 68°9.9Ω + 5.4Ω
Philips Semiconductors Application note
AN95021433MHz front-end with the SA601 or SA620
1995 Mar 3 4–3
2.1 Application circuit
The application circuit diagram is shown in Figure 2.
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
Vcc
GND
LNA IN
GND
GND
MIXER PD
GND
LO IN
LO IN
Vcc
GND
LNA OUT
GND
MIXER IN
GND
MIXER OUT
MIXER OUT
GND
GND
Vcc
C1
L1
56nH
100pF
C3
100pF
VCC
100 SA601
R1
U1
VCC
J1
C2
100nF
VCC
MIXER OUT
J3
45MHz
10pF
C9
50Ω
RF IN
433MHz
GND
C6
100pF
C5
100nF
VCC
C4
100pF
C8
100pF
C7
6p8
22pF
C10
C11
100pF
50Ω
L2
620nH L3
330nH
Figure 2. Application Circuit Diagram
Table 2. SA601 Application Components
C1 DC blocking C9 Mixer output current
combiner
C2 T ime constant for LNA
compensation loop C10 Mixer output match to
50Ω load
C3 VCC decoupling C11 VCC decoupling
C4 DC blocking R1 LO input match
C5 Vcc decoupling L1 AC blocking
C6 Vcc decoupling L2 Mixer output current
combiner
C7 LNA to Mixer input
match L3 Mixer output current
combiner
C8 DC blocking
Table 2 shows that most of the external components are for blocking
DC at the in- and outputs and decoupling of the power supply. In
your actual receiver the DC-blocking capacitors for RF IN, LO IN
and MIXER OUT can be removed if there is no DC path present.
Capacitor C2 determines the bandwidth of the compensation loop of
the LNA. The LNA is stabilized for temperature and power supply
variations. To achieve a compensation loop which controls the LNA
gain, the bandwidth of this control loop must be low compared to the
actual input frequency. Otherwise the compensation loop and, thus,
the LNA gain would be affected by the RF input signal.
To isolate C2 from the LNA input for 433MHz signals an inductor L1
is included. This forms a short for the compensation loop
frequencies and an open for the 433MHz frequencies.
If there is already a DC path at the LNA input (J1) to ground, then L1
and C2 can be omitted. In that case C1 must be increased to
100nF. C1 has two functions then: block DC from the LNA input,
and determine the bandwidth of the compensation loop.
The LNA output is matched to the Mixer input with a 6.8pF capacitor
(C7) to ground and a series inductor of 9nH. This inductor is
realized by the traces between LNA out and Mixer and the
inductance of C8.
The SA601 mixer has differential outputs. This means that a direct
interface with a symmetrical filter or symmetrical gain stage is
possible. However, most filters are asymmetrical, therefore, a
transformation from dif ferential to single-ended is required. With a
current combiner circuit1, the differential output currents are shifted
such that they are in phase. These currents are then combined to
create a single-ended output. L2, L3 and C9 form this current
combiner circuit.
The inductor can be calculated as follows:
•Choose a value for C9: 10pF
•F is 45MHz
•Calculate L for appropriate current combining
F1
2L2C
L1
(2F)22C1
(245MHz)210pF
L625nH
1. A current combiner circuit for better mixer conversion gain,
Sheng Lee, Alvin K. Wong, Michael G. Wong, Philips
Semiconductors
Philips Semiconductors Application note
AN95021433MHz front-end with the SA601 or SA620
1995 Mar 3 4–4
Figure 3 shows the implementation of the calculated component
values.
VCC
625nH 625nH
10pF
PIN 14 PIN 13
Figure 3. Current Combiner Circuit
After designing the current combiner circuit, the next step is to
match the mixer output to the impedance of the load. In the
application circuit the load is assumed to be 50 Ω. This is done to
make evaluation more simple since most RF measurement
equipment have 50 Ω inputs.
In addition to the impedance of the load (50 Ω), it is also important to
know what the optimum load impedance is for the mixer output. For
the SA601 mixer output this is 600 Ω. To create a matching from 600
to 50 Ω the circuit from Figure 4 is applied.
VCC
645nH
21pF
600Ω50Ω
Figure 4. Mixer Output Match to 50Ω Load
The circuits from Figures 3 and 4 can be merged into one circuit as
is shown in Figure 5. The values between brackets are the actual
component values applied in the application circuit diagram.
VCC
625nH 625nH//645nH = 317nH
10pF
PIN 14 PIN 13 21pF
(22pF)
50Ω
(620nH) (330nH)
Figure 5. Mixer Output Circuitry With Current Combiner and
50Ω Matching
2.2 Measurement Results
For the measurements a power supply of 3V is applied. The RF
frequency is 433MHz and the LO frequency is 478MHz with a level
of -7dBm.
The current consumption of this application is 7.8mA.
2.2.1 Conversion gain, Noise Figure and IP3
In Table 3 the performance of the LNA and mixer is shown together
with the overall performance.
Table 3. LNA, Mixer Measurement Results
LNA Mixer LNA &
Mixer Units
Gain 15.4 9.2 24.7 dB
Noise
Figure 1.5 12 2.5 dB
IIP3 -14.3 +1.7 -18.1 dBm
The results show that this Front-End offers 25dB of power gain with
a noise figure contribution of only 2.5dB at 433MHz.
2.2.2 Isolation
Another important parameter for a Front-End receiver is the isolation
between the Local Oscillator and the Antenna (LNA input). For
433MHz applications the requirement2 is that spurious signals
generated by the receiver have a maximum level of -57dBm for
frequencies below 1GHz. The LO level measured at the LNA input
is -53dBm. This means only 4dB extra suppression is required to
meet the requirements. Because the Local Oscillator is offset
45MHz of the RF frequency, a simple bandpass filter, or the
selectivity of the antenna, is already sufficient.
3. SA620
The SA620 comprises a 1.2GHz LNA, Mixer and VCO. The block
diagram is shown in Figure 6. In a receiver the SA620 performs the
amplification of the antenna signal and the down conversion to the
first IF frequency. The VCO can be part of a phase-lock-loop or set
to a fixed frequency by using a resonator. The output signal of the
mixer can be handled by an IF system like the SA676 which takes
care of AM and FM demodulation.
The S-parameters of the LNA and mixer input are the same as for
the SA601. These parameters are shown in Table 1.
The LNA performance of the SA620 is the same as for the SA601.
The mixer performance, however, is different. This is due to the
output structure of the mixer. Figure 6 shows that there is one mixer
output. Remember the SA601 has 2 mixer outputs which were
combined using the current combiner circuit. Therefore, the mixer
conversion gain is higher for the SA601 mixer. Furthermore, the
SA620 incorporates a buffered VCO output (Pin 11) which can be
used to drive the input of a frequency synthesizer.
3.1 Application circuit
Figure 7 shows the application circuit for a 433MHz receiver with a
478MHz VCO design.
2. ETSI I-ETS 300 220 Annex A.1.3.
Philips Semiconductors Application note
AN95021433MHz front-end with the SA601 or SA620
1995 Mar 3 4–5
43215
20 19 18 17 16
761098
15 14 13 12 11
MIXER OSC
PWRDN OSC1 OSC2
VCC LNA LNA
BIAS MIXER
IN MIXER
GND MIXER
OUT OSC
GND VCO
OUT
LNA
LO
VCO
RF IF
LNA
ENABLE LNA
GND LNA IN LNA OSC
GND
AUTOMATIC
LEVELING
LOOP
TRACKING
BANDPASS
FILTER
GND LNA
OUT
GND LNA
GND PWRDN
MIXER
BYPASS
Figure 6. SA620 Block Diagram
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
LNA ENABLE
GND
LNA IN
GND
GND
MIXER PD
OSC PD
OSC1
OSC2
Vcc
GND
LNA OUT
LNA BIAS
MIXER IN
GND
MIXER BYPASS
MIXER OUT
GND
GND
VCO OUT
SA620
U1
RF IN
433MHz
100pF
C1
J1
C2
100nF
L1
56nH
C5
100nF C6
100pF
C7
6p8
50Ω
MIXER OUT
45MHz
50Ω
C13
100pF
C14
4.7pF
L4
8.2nH
C12
100nF
C9
100nF
C15
2.2pF D1
R1
10k
R2
10k
C16
100nF
VCONTROL
VCC
VCO OUT
R3
22
C17
100pF J2
J3
C10
22pF
L3
620nH
VCC
C11
100pF
VCC
VCC
GND
C8
100pF
C18
100pF
Figure 7. Application Circuit Diagram
Table 4 shows that most of the external components are for blocking
DC at the in- and outputs and decoupling of the power supply. In
your actual receiver the DC-blocking capacitors for RF IN, LO IN
and MIXER OUT can be removed if there is no DC path present.
As with the SA601 capacitor, C2 determines the bandwidth of the
compensation loop of the LNA. The LNA is stabilized for
temperature and power supply variations. To achieve that a
compensation loop controls the LNA gain. The bandwidth of this
control loop must be low compared to the actual input frequency.
Otherwise the compensation loop and, thus, the LNA gain, would be
affected by the RF input signal. To isolate C2 from the LNA input for
433MHz signals, an inductor L1 is included. This forms a short for
the compensation loop frequencies and an open for the 433MHz
frequencies.
Philips Semiconductors Application note
AN95021433MHz front-end with the SA601 or SA620
1995 Mar 3 4–6
Table 4. SA620 Application Components
C1 DC blocking
C2 T imeconstant for LNA compensation loop
C5 VCC decoupling
C6 VCC decoupling
C7 LNA to Mixer input match
C8 DC blocking
C9 Mixer Bias decoupling
C10 Mixer output match to 50 Ω load
C11 VCC decoupling
C12 VCO Bias decoupling
C13 VCC decoupling
C14 T uning capacitor
C15 Limits tuning range of VCO
C16 Filters noise at Vcontrol line
C17 DC blocking
C18 VCC decoupling
L1 AC blocking
L3 Mixer output match to 50 Ω load
L4 T uning inductor
R1 Prevents loading of Tank circuit by the Vcontrol line
R2 Filters noise at Vcontrol line
D1 Varactor SMV 1204-099 Alpha Industries
If there is already a DC path at the LNA input (J1) to ground, then L1
and C2 can be omitted. In that case, C1 must be increased to
100nF. C1 has two functions then: block DC from the LNA input,
and determine the bandwidth of the compensation loop.
The LNA output is matched to the Mixer input with a 6.8pF capacitor
(C7) to ground and a series inductor of 9nH. This inductor can be
realized by the traces between LNA Out and Mixer In and the
parasitic inductance of C8.
The mixer output is matched to 50 Ω at 45MHz with L3 and C10.
The VCO output, Pin 11, delivers -20dBm into a 50 Ω load. The
output level is set with R3. A lower output level can be achieved by
reducing the value of this resistor. A higher value for R3 is not
recommended because this will affect the VCO performance.
The components that determine the actual frequency of the VCO are
L4, C14, C15 and D1 according to:
F+1
2@@L4@ǒC14 )ǒC15@CD1
C15)CD1ǓǓ
Ǹ
Figure 8.
The formula shows that the influence of the varactor D1 on the VCO
frequency depends on the value of C15. That means that, if the
tuning range of the VCO is too wide, it can be scaled back by
reducing the value of C15.
The SA620 VCO can easily oscillate from 300 to 1.2GHz, so it is
important to have only one resonance circuit at Pins 9 and 10. Also,
parasitic resonances must be prevented, which can be
accomplished by putting the components close to Pins 9 and 10,
and by decoupling the power supply close to L4 and C14.
3.2 Measurement Results
For the measurements a power supply of 3V is applied. The RF
frequency is 433MHz and the VCO frequency is tuned to 478MHz.
The current consumption of this application is 11.3mA.
3.2.1 Conversion gain, Noise Figure and IP3
In Table 5 the performance of the LNA and mixer is shown together
with the overall performance.
Table 5. Measurement Results
LNA Mixer LNA &
Mixer Units
Gain 15.5 4.5 19.5 dB
Noise
Figure 1.5 8.5 2.6 dB
IIP3 -14.2 0.0 -18.5 dBm
The results show that this Front-End offers 19.5dB of power gain
with a noise figure contribution of 2.6dB at 433MHz.
3.2.2 Isolation
The isolation between the LO signal and antenna input is -59dBm.
The requirement3 for 433MHz ISM band is -57dBm at the antenna
input for signals outside the 433MHz band and below 1GHz. This
means that, without any selectivity at the antenna input, this
requirement is already met. In practice there will be selectivity from
the antenna filter or the antenna itself, meaning the LO signal is
further suppressed.
4. CONCLUSION
The advantages of using the SA601 or SA620 as a 433MHz Front
End are:
•Ease of design
•Good performance
•Minimum amount of external components
•Power supply operation from 2.7 to 5.5V
When there is an external Local Oscillator available, the SA601 is
the best choice because it has higher overall gain than the SA620.
This is because the SA601 mixer has a differential mixer output.
The SA620 has the benefit of having a VCO on-chip. With this VCO
the LO frequency is generated, so no extra VCO module is required.
Both the SA601 and SA620 come in an SSOP20 and are in full
volume production.
3. ETSI I-ETS 300 220 Annex A.1.3.
