32 general description rf antenna/rf amplifier protection against esd events is a growing concern of rf circuit designers today, given the combination of increased signal gain demands, coupled with the required downsizing of the transistor package. the ability to achieve both objectives is tied to a reduced thickness of the sio 2 gate insulator layer within the semiconductor. the corresponding result of such a change increases the power amplifiers (pas) vulnerability to esd strikes a common event with handheld electronic products with rf transmitting and/or receiving features. avxs 0402/0603 antennaguard products are an ultra-low capacitance extension of the proven transguard ? tvs (transient voltage suppression) line of multilayer varistors. rf designers now have a single chip option over conventional protection methods (passive filters with diode clamps), which not only gives superior performance over traditional schemes, but also provides the added benefits of reduced pcb real estate and lower installation costs. avxs antennaguard products are available in capacitance ratings of 3pf (0402 & 0603 chips) and 12pf (0603 chip). these low capacitance values have low insertion loss, as well as give other transguard ? advantages such as small size, sub-nanosecond response time, low leakage currents and unsurpassed reliability (fit rate of 0.2) compared to diodes. ? smallest tvs component ? standard eia chip sizes ? chip placement compatible ? fastest response time to esd strikes ? two cap values (3 and 12pf) ? esd protection for rf amplifiers ? laser drivers features application how to order vc 04 ag 18 3r0 y a t x x varistor chip size varistor series working capacitance non-std. not termination reel reel chip 04 = 0402 antennaguard voltage 3pf = 3r0 cap applicable t = ni/sn alloy size quantity 06 = 0603 (dc) 12pf = 120 tolerance (plated) 1 = 7" a = 4,000 (maximum) 3 = 13" or 10,000 w = 7" (0402 only) (i.e., 1a = 4,000 3a = 10,000) wa = 10,000 antennaguard 0402/0603 avx multilayer ceramic transient voltage suppressors esd protection for antennas and low capacitor loading applications
33 antennaguard catalog part numbers/electrical values avx part number v w (dc) v w (ac) i l cap case size elements vc04ag183r0yat_ _ 18 14 0.1 3 0402 1 vc06ag183r0yat_ _ 18 14 0.1 3 0603 1 vc06ag18120yat_ _ 18 14 0.1 12 0603 1 physical dimensions 0402 0603 length 1.0 (0.039) 0.1 (0.004) 1.6 (0.063) 0.15 (0.006) width 0.5 (0.020) 0.1 (0.004) 0.8 (0.031) 0.15 (0.006) thickness 0.6 max. (0.024) 0.9 max. (0.035) termination band width 0.25 (0.010) 0.15 (0.006) 0.35 (0.014) 0.15 (0.006) mm (inches) antennaguard 0402/0603 avx multilayer ceramic transient voltage suppressors esd protection for antennas and low capacitor loading applications termination finish code packaging code v w (dc) dc working voltage (v) v w (ac) ac working voltage (v) i l maximum leakage current at the working voltage (a) cap maximum capacitance (pf) @ 1 mhz and 0.5 vrms; vc06ag18120yat capacitance tolerance: +4, -2pf
34 mm (inches) antenna varistors avx offers a series of 0402 and 0603 chip varistors, designated the antennaguard series, for rf antenna/rf amplifier protection. these devices offer ultra-low capaci- tance (<3pf in 0402 chips, and 3pf & 12pf in 0603 packages), as well as low insertion loss. antenna varistors can replace output capacitors and provide esd suppression in cell phones, pagers and wireless lans. it is very common to employ some form of a fet in many types of efficient/miniature rf amplifiers. typically, these rf transistors have nearly ideal input gate impedance and outstanding noise figures. however, fets are very suscepti- ble to esd damage due to the very thin layer of sio 2 uses as the gate insulator. the ultra-thin sio 2 layer is required to improve the gain of the transistor. in other words, the upside of the performance enhancement becomes the downside of the transistors survival when subjected to an esd event. esd damage to the rf field effect transistors (fets) is a growing concern among rf designers due to the following trends: (1) rf amplifiers continue to shrink in size, and (2) fet gains figures continue to increase. both trends relate to decreasing gate oxide thickness, which in turn, is directly proportional to increased esd sensitivity. as miniaturization trends accelerate, the traditional methods to protect against esd damage (i.e., pc board layout, passive filters, and diode clamps) are becoming less and less effective. avxs antennaguard varistor can be used to protect the fet and offer superior performance to the previously mentioned protection methods given above. the standard eia 0603 chip size, and particularly the 0402 chip, offer designers an esd protection solution consistent with todays downsizing trend in portable electronic products. savings in component volume up to 86%, and pc board footprint savings up to 83% are realistic expectations. these percentages are based upon the following table and figures 1a and 1b. d2 d3 d1 d5 d4 0.96 (0.037) 0.96 (0.037) 2.0 (0.079) 0.8 (0.031) mm (inch 0.9 (0.035) pad dimensions suppression device d1 d2 d3 d4 d5 avx 0402 transguard ? 1.70 (0.067) 0.61 (0.024) 0.51 (0.020) 0.61 (0.024) 0.51 (0.020) avx 0603 transguard ? 2.54 (0.100) 0.89 (0.035) 0.76 (0.030) 0.89 (0.035) 0.76 (0.030) competitors sot23 diode see below figure 1a. 0402/0603 ir solder pad layout figure 1b. sot23- solder pad layout antennaguard 0402/0603 avx multilayer ceramic transient voltage suppressors esd protection for antennas and low capacitor loading applications
35 antenna varistors offer excellent esd repetitive strike capa- bility compared to a sot23 diode when subjected to iec 61000-4-2 8kv contact discharge. a performance summary is shown in figure 2. antenna varistors also turn on and divert esd overvoltages at a much faster rate than sot23 devices (typically 300ps vs 1500ps - 5000ps). see figure 3. typical implementations of the antenna varistors are shown for use in cell phone, pager and wireless lan applications in figures 6a, 6b and 6c. the equivalent circuit model for a typical antenna varistor is shown in figure 4. the varistor shown exhibits a capacitance of 3pf which can be used to replace the parallel capacitance typically found prior to the antenna output of an rf amplifier. in the off state, the varistor acts as a capacitor and helps to filter rf output. the varistor is not affected by rf output power or voltage and has little insertion loss. see figure 3. 0603 - 12pf 0603 - 3pf 0402 - 3pf 520 70 60 50 40 30 20 10 0 500 480 460 breakdown voltage (vb) 0402 & 0603 3pf ratings breakdown voltage (vb) 0603 12pf rating 440 420 400 380 0 100 8kv esd strikes 1000 10,000 figure 2. repetitive 8kv esd strike figure 5. antenna vs frequency figure 3. turn on time figure 4. antenna varistor figure 6a. cell phone figure 6b. pager 100% 90% 30ns 1ns 30ns time (ns) 60ns 60ns mlv turn on time 300ps to 700ps peak sitvs turn on time 1.5ns to 5ns l n r v r i c 1 l n = body inductance c 1 = device capacitance r v = voltage variable resistor r i = insulation resistance vc04ag183r0 vc06ag183r0 vc06ag18120 0.01 0.1 1.0 10 frequency (ghz) db 0 -5 -10 -15 -20 -25 -30 fet 2.2pf 2.7pf 12pf 3pf varistor fet esd test of antennaguard ratings antenna varistor s21 antennaguard 0402/0603 avx multilayer ceramic transient voltage suppressors esd protection for antennas and low capacitor loading applications figure 6c. 35
|
