DN515 - High Input IP3 Mixer Enables Robust VHF Receivers

High Input IP3 Mixer Enables Robust VHF Receivers
Design Note 515
Andy Mo
Introduction
An increasing number of applications occupy the
30MHz to 300MHz very high frequency (VHF)
band. Television and radio broadcasting, navigation
controls and amateur radios are a few examples.
Modern RF component development is aimed at
much higher frequency bands used for voice and
data communications systems. Significant advance
in circuit techniques and manufacturing processes
are required to meet the demanding performance
requirements of the next generation of radios. Applying
these techniques to lower frequency designs can
significantly improve performance.
implementations, the LTC5567 contains integrated
RF and LO transformers. The Input IP3 linearity
performance benchmark is an excellent 30dBm for
the LTC5567 in its specified frequency range. Going
lower in frequency requires the built-in transformers
to maintain this linearity as well as conversion gain.
With such a high level of linearity to start from, it
is worthwhile to modify the mixer circuit design
and characterize the performance over lower VHF
frequencies. The proof of performance is in the testing.
Impedance Match Design
Figure 1 shows an impedance match design with the
LTC5567. Table 1 shows the design values extending
input port match below 300MHz, down to 150MHz,
The LTC ®5567 is a wideband mixer designed and
optimized for performance in the 300MHz to 4GHz
frequency band. To create very compact circuit
L4
LO IN
C6
C5
1000pF
16
GND
TEMP
RF IN
50Ω
L, LT, LTC, LTM, Linear Linear Technology, and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
1
C3
1000pF
2
L3
C4
3
4
TEMP
15
LO
14
C7
33pF
13
NC GND
LTC5567IUF
GND
12
GND
11
IF+
RF
IF–
GND
GND
10
9
T1
3 TC4-1W 4
L1
510nH VCC
L2
510nH
C2
10nF
2
1
IF OUT
39MHz TO 73MHz
50Ω
6
EN VCC NC IADJ GND
5
EN
6
7
8
17
C8
33pF
C1
10nF
VCC
C9
1µF
10V
0603
VCC
3V TO 3.6V
DN515 F01
Figure 1. VHF Mixer Design
Table 1. VHF Impedance Match Design Values
06/13/515
MATCH
RF INPUT
L3
C4
LO INPUT
L4
C6
A
150MHz
8.2nH
56pF
200MHz
3.9nH
47pF
B
200MHz
6.8nH
39pF
250MHz
2.7nH
33pF
C
250MHz
3.9nH
27pF
300MHz
1.5nH
27pF
while still achieving outstanding performance. Test
results are also provided.
Figure 2 shows the LTC5567 mixer gain and input IP3
versus input frequency. The mixer linearity performance
improves as input frequency approaches 150MHz. Input, LO and output port return loss measurements are
shown in Figures 3, 4 and 5, respectively. The overall
performance is maintained in the VHF range compared
to higher input frequencies. As a result, the high IP3
and conversion gain yields maximum dynamic range
when used in radio designs. Higher dynamic range
minimizes adjacent channel interference, improving
selectivity. Operating the LTC5567 below 150MHz
input is possible with reduced conversion gain, but
not recommended, due to the internal transformer
becoming lossy.
Conclusion
The LTC5567 offers very high linearity performance
at VHF and UHF input frequencies. High IP3 figures
and P1dB in (Table 2) make it an excellent choice for
high performance radio design over a wide range of
frequencies.
0
35
INPUT IP3 (dBm)
–2
–4
25
20
RETURN LOSS (dB)
GAIN (dB), IIP3 (dBm)
30
PLO = 0dBm, HIGH SIDE LO
PRF = –6dBm (–6dBm/TONE
FOR 2-TONE IIP3 TESTS,
∆f = 2MHz)
15
10
5
–5
150
–14
170
190
230
210
INPUT FREQUENCY (MHz)
250
0
0
50
100
200
150
FREQUENCY (MHz)
DN515 F05
Figure 5. IF Output Return Loss
Table 2. P1dB Compression Point and LO Leakage
Over Input Frequency. Output Frequency = 50MHz,
HSLO
–5
RETURN LOSS (dB)
–16
DN515 F02
Figure 2. Mixer IIP3 and Gain Performance Results
–10
–15
–20
–25
–30
MATCH A
MATCH B
MATCH C
–35
50
100
150 200 250 300
FREQUENCY (MHz)
350
400
DN515 F03
Figure 3. RF Input Return Loss
0
RETURN LOSS (dB)
–10
–12
GAIN (dB)
0
–40
–6
–8
RF INPUT FREQUENCY
(MHz)
P1dB
(dBm)
LO TO IF LEAKAGE
(dBm)
150
12.29
–35
160
12.9
–42
170
12.9
–42
180
12.75
–42
190
12.70
–41.2
200
11.61
–43
210
12.48
–43
–5
220
12.7
–44
–10
230
11.7
–44
–15
240
11.08
–44
–20
250
12.89
–44
MATCH A
MATCH B
MATCH C
–25
–30
50
100
150 200 250 300
FREQUENCY (MHz)
350
400
DN515 F04
Figure 4. LO Input Return Loss
Data Sheet Download
www.linear.com/LTC5567
Linear Technology Corporation
For applications help,
call (408) 432-1900
dn515f LT/AP 0613 196K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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 LINEAR TECHNOLOGY CORPORATION 2013
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