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 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2013