Datasheet HSMS-282x (Broadcom) - 5

Applications Information
8.33 X 10 -5 nT R
Product Selection
j = –––––––––––– = R V – R s I S + I b Avago’s family of surface mount Schottky diodes provide unique solutions to many design problems. Each is opti‑ 0.026 ≈ ––––– at 25 °C mized for certain applications. I S + I b The first step in choosing the right product is to select the where V - IR S ––––– diode type. All of the products in the HSMS‑282x fami‑ 0.026 n = idealit I = I S y fac (e tor (see table of SPICE par – 1) ameters) ly use the same diode chip–they differ only in package T = temperature in °K configuration. The same is true of the HSMS‑280x, ‑281x, I = saturation current (see table of SPICE parameters) 285x, ‑286x and ‑270x families. Each family has a different S I = externally applied bias current in amps set of characteristics, which can be compared most easily b R = sum of junction and series resistance, the slope of by consulting the SPICE parameters given on each data v the V‑I curve sheet. I is a function of diode barrier height, and can range from The HSMS‑282x family has been optimized for use in RF S picoamps for high barrier diodes to as much as 5 µA for applications, such as very low barrier diodes. • DC biased small signal detectors to 1.5 GHz. 8.33 X 10 -5 nT
The Height of the S
R j =
chottky Barrier
–––––––––––– = R V – R s • Biased or unbiased large signal detectors (AGC or I The current‑voltage char S + I b acter istic of a Schottky barrier power monitors) to 4 GHz. diode at room t 0.026 emperature is described by the following ≈ ––––– at 25 °C • Mixers and frequency multipliers to 6 GHz. equation: I S + I b The other feature of the HSMS‑282x family is its unit‑to‑unit V - IR and lot‑to‑lot consistency. The silicon chip used in this se‑ S ––––– I = I 0.026 – 1) ries has been designed to use the fewest possible process‑ S (e ing steps to minimize variations in diode characteristics. On a semi‑log plot (as shown in the Avago catalog) the Statistical data on the consistency of this product, in terms current graph will be a straight line with inverse slope 2.3 of SPICE parameters, is available from Avago. X 0.026 = 0.060 volts per cycle (until the effect of R is seen S For those applications requiring very high breakdown in a curve that droops at high current). All Schottky diode voltage, use the HSMS‑280x family of diodes. Turn to the curves have the same slope, but not necessarily the same HSMS‑281x when you need very low flicker noise. The value of current for a given voltage. This is deter mined HSMS‑285x is a family of zero bias detector diodes for small by the saturation current, I , and is related to the barrier S signal applications. For high frequency detector or mixer height of the diode. applications, use the HSMS‑286x family. The HSMS‑270x Through the choice of p‑type or n‑type silicon, and the is a series of specialty diodes for ultra high speed clipping selection of metal, one can tailor the characteristics of a and clamping in digital circuits. Schottky diode. Barrier height will be altered, and at the
Schottky Barrier Diode Characteristics
same time C and R will be changed. In general, very low J S Stripped of its package, a Schottky barrier diode chip con‑ barrier height diodes (with high values of I , suitable for S sists of a metal‑semiconductor barrier formed by deposi‑ zero bias applica tions) are realized on p‑type silicon. Such tion of a metal layer on a semiconductor. The most com‑ diodes suffer from higher values of R than do the n‑type. S mon of several different types, the passivated diode, is shown in Figure 10, along with its equivalent circuit.
R METAL S
R is the parasitic series resistance of the diode, the sum S of the bondwire and leadframe resistance, the resistance
PASSIVATION PASSIVATION
of the bulk layer of silicon, etc. RF energy coupled into R
N-TYPE OR P-TYPE EPI LAYER
S is lost as heat—it does not contribute to the rectified out‑
Rj SCHOTTKY JUNCTION Cj
put of the diode. C is parasitic junction capaci tance of the
N-TYPE OR P-TYPE SILICON SUBSTRATE
J diode, controlled by the thick‑ness of the epitaxial layer and the diameter of the Schottky contact. R is the junc‑
CROSS-SECTION OF SCHOTTKY EQUIVALENT
j
BARRIER DIODE CHIP CIRCUIT
tion resistance of the diode, a function of the total current
Figure 10. Schottky Diode Chip.
flowing through it. 5