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 advances 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

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