《RF_balun_transformer》由会员分享，可在线阅读，更多相关《RF_balun_transformer（4页珍藏版）》请在金锄头文库上搜索。
1、IntroductionThis application note is designed to help the readerunderstand how balun transformers can be used intodays RF/Microwave communication applications. Thereis an increasing demand for balun transformers in todaystelecommunication market and M/A-COM is leading thefield with this device. As m
2、any as six of this device canbe used around any particular chip as illustrated in figure4. M/A-COMs balun transformer can be classified intotwo groups A) The flux coupled balun transformer and B)The transmission line balun transformer.Definition of TermsInsertion Loss (dB): Loss due to transmission
3、fromprimary dot port to secondary dot port and secondaryport. Most balun transformers are symmetrical throughtheir central horizontal axis, therefore, an input can beapplied at the primary dot port or the primary port withdifferential outputs at the secondary dot and secondaryports.Amplitude Balance
4、 (dB): Measure of the difference inamplitude between the two differential outputs.Phase Balance (degrees): Measure of the difference inphase between the two differential outputs, i.e. measuredfrom 180.Return Loss (dB): Loss due to reflection at any port.Figure 2. 4:1 Transmission Line Balun Transfor
5、merM/A-COM Division of AMP Incorporated n North America: Tel. (800) 366-2266, Fax (800) 618-8883 n Asia/Pacific: Tel. +85 2 2111 8088, Fax +85 2 2111 8087n Europe: Tel. +44 (1344) 869 595, Fax +44 (1344) 300 AMP and Connecting at a Higher Level are trademarks.Specifications subject to change withou
6、t notice.10-25RF Balun TransformersM565Application NoteV2.00Figure 3. 1:1 Transmission Line Balun TransformerA. Flux Coupled Balun TransformersThe flux coupled balun transformer can provide a widerange of impedance ratios; 1:1, 4:1, 9:1 and 16:1 are mostcommon. DC isolation from primary coil to seco
7、ndary coilis also a feature of this device. It has a low loss and goodbalance over a broad frequency bandwidth. The ETC4-1-2has an insertion loss of approximately 2.5 dB at 800 MHzand is an example of one of our most popular fluxcoupled balun transformers.B. Transmission Line Balun TransformersThe t
8、ransmission line balun transformer comes in twoimpedance ratios as outlined above, i.e. 4:1 and 1:1. Itoperates at higher frequencies and over a greaterbandwidth than the flux coupled balun transformer. Itcannot provide DC isolation from primary side tosecondary side. The ETC1.6-4-2-3 is an example
9、of one ofour most popular 4:1 transmission line balun transformerswith an optimum performance of 1 dB insertion loss at900 MHz.ApplicationsThe applications of these devices are:1. Impedance matchingSee figure 5. The inputs to the LO buffer amplifier andthe quad diode ring are at 100 W approximately.
10、2. DC isolationSee figure 5. At DC there is no magnetic coupling,therefore, the LO balun transformer and the RF baluntransformer are acting as open circuits at DC.3. Matching balanced ports to a single ended portSee figure 6. The inputs to the diode pair are 180 out ofphase.The flux coupled balun tr
11、ansformer can incorporate all ofthe above, whereas the transmission line baluntransformer cannot provide DC isolation. Matching singleended ports to balanced (differential) ports on anFigure 1. Flux Coupled Balun TransformerM/A-COM Division of AMP Incorporated n North America: Tel. (800) 366-2266, F
12、ax (800) 618-8883 n Asia/Pacific: Tel. +85 2 2111 8088, Fax +85 2 2111 8087n Europe: Tel. +44 (1344) 869 595, Fax +44 (1344) 300 AMP and Connecting at a Higher Level are trademarks.Specifications subject to change without notice.10-26integrated circuit is a common application of thesedevices. Figur
13、e 4 shows the first mixer stage and secondmixer stage of a receiver chip functional block diagramthat is commonly used in digital radio applications. Here are the differential ports associated with the chip infigure 4; Differential outputs from second local oscillator buffer amplifier 1+LOB1LOB1 Sec
14、ond local oscillator differential inputs+2LOIN2LOIN Differential IF inputs+IFINIFIN Differential outputs from first mixer+MXOUTMXOUT Differential inputs to first mixer+MXINMXINRF Balum Transformers M565V2.00 Differential inputs to first local oscillator+1LOIN1LOIN Differential outputs from second lo
15、cal oscillator bufferamplifier 2+LOB2LOB2“Passive matching” refers to the use of a ferrite woundtransformer “off chip” to do this job, while “activematching” incorporates the transformer (or matchingdevice) on the chip. The advantage of active matching isthat there is a cost reduction due to the abs
16、ence of theferrite wound transformers, but the chip then becomesvery specific, also the quality of this matching will not beas good as the matching that a passive transformer wouldprovide. Passive matching allows the design engineer todesign a chip that could cover more than one application,i.e. his design is more versatile. Also, matching at IF frequencies for GSM, for DCS, PCSand WLAN, for example, can be extremely awkw
