Robert Noyce independently devised the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it. In tunnel diode, electric current is … This is called negative differential resistance because current decreases with increasing voltage. 2. I want to use a tunnel diode to implement a simple van der pol oscillator circuit. Plot energy against V. Why can I not shoot as sharp as I see on live preview? Ponder. Current Components in a Tunnel Diode. It was introduced by Leo Esaki in 1958.Heavily-doped p-n junction. [8]:7–35 Their low capacitance allows them to function at microwave frequencies, far above the range of ordinary diodes and transistors. Thus, charge carriers do not need any kinetic energy to move across the junction; they simply punch through the junction. Useful comment in [oscillator applications](http://www.powerguru.org/crystal-oscillator- I. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. tum tunnel over a classically forbidden barrier. Thus, it is called Tunnel diode. Tunnel diodes are susceptible to damage by overheating, and thus special care is needed when soldering them. I have 2 identical overhead projectors with bad diodes, but the diodes have different numbers. In the tunnel diode, the dopant concentrations in the P and N layers are increased to a level such that the reverse breakdown voltage becomes zero and the diode conducts in the reverse direction. The equivalent circuit of the tunnel diode is expressed in the figure below. MathJax reference. In a conventional semiconductor diode, conduction takes place while the P-N junction is forward biased and blocks current flow when the junction is reverse biased. Does anyone know the equation that relates current to voltage for a specific tunnel diode(can be any tunnel diode)? [9], Another type of tunnel diode is a metal–insulator–insulator–metal (MIIM) diode, where an additional insulator layer allows "step tunneling" for more precise control of the diode. A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively "negative resistance" due to the quantum mechanical effect called tunneling. Firstly, it reduces the width of the depletion layer to an extremely small value (about 0.00001 mm). Due to their low output power, tunnel diodes are not widely used: Their RF output is limited to a few hundred milliwatts due to their small voltage swing. Hope that helps. The working theory of this special configuration is actually amazingly straightforward. 1 Mechanism of Tunneling 1 3. how to calculate recombination lifetime for holes for a specific diode? 1 Hybrid Technique 40 4. 2 Diode Circuit Parameters 2 3. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as Sony. I doubt if this equation is especially useful but it does allow you to get a rough model of a real device. Tunnel diodes are also more resistant to ionizing radiation than other diodes. The most important operating region for a tunnel diode is the "negative resistance" region. Can this equation be solved with whole numbers? where is the Richardson constant and f B is the Schottky barrier height which equals the difference between the Fermi level in the metal, E F,M and the conduction band edge, E c, evaluated at the interface between the metal and the semiconductor.The -1 term is added to account for the current flowing from right to left. Axis units are semi arbitrary - adjust parameters to suit. 6 Biasing Technique 14 4. In recent years, however, new devices that use the tunneling mechanism have been developed. Their "negative" differential resistance in part of their operating range allows them to function as oscillators and amplifiers, and in switching circuits using hysteresis. A Tunnel diode is a heavily doped p-n junction diode in which the electric current decreases as the voltage increases.. 4 Measurement of Diode Parameters 9 3. The R s represents the resistance of the connecting leads of the diode and the semiconductor material. Specific device parameters for this model: VP=50mV; Ip=5mA; Vv=370mV; IV=370uA; Vpp=525mV Current flow in … Windows 10 Wallpaper, Ceramic resonator changes and maintains frequency when touched. A tunnel diode has a negative resistance in the voltage region where tunneling takes place. Wow! The conventional current equation for a diode is expressed as () = e x p ( ()) − 1, (2) where () is the voltage across the diode, is the reverse saturation current, and is a parameter representing the slope of the conductance curve of the diode characteristic. This was made "by eye" solely on the basis of approximating an Esaki diode V/I curve. There's more, but that's enough OTW already :-). It allows us to make predictions about wave functions. (vintage audio amplifier), Origin of the Liouville theorem for harmonic functions. It only takes a minute to sign up. Here Ip-Peak current. Unlike most other devices you cxan have the same current at 3 different voltages - with two being stable, and the intermediate voltage being a transient one due to it being in a region of negative resistance. Ni/NiO/Ni tunnel diodes. Next, letting x 1 ( t ) = v c ( t ) and x 2 ( t ) = i L ( t ) be the state variables, the circuit is governed by the following state equations: Under reverse bias, filled states on the P-side become increasingly aligned with empty states on the N-side, and electrons now tunnel through the P-N junction barrier in reverse direction. The formula is shown below the graph. design-and-negative-resistance/), Here is a completely made up example. 3. The Schrӧdinger equation is the fundamental equation of wave quantum mechanics. Is there a mod that can prevent players from having a specific item in their inventory? 3 Diode Construction 8 3. This heavy doping produces following three unusual effects: 1. [10] There is also a metal–insulator–metal (MIM) diode, but due to inherent sensitivities, its present application appears to be limited to research environments.[11]. Such amplifiers were considered state-of-the-art, with better performance at high frequencies than any transistor-based front end. P-N Diodes in series. Quantum tunneling occurs because there exists a nontrivial solution to the Schrödinger equation in a classically forbidden region, which corresponds to the exponential decay of the magnitude of the wavefunction. So far I found a SPICE code for 1N4393 from this reference. Further voltage increase (from approx. Index Terms—Asymmetric tunneling diode, infrared energy conversion, metal–insulator–metal (MIM) tunneling diode, rectifier. Is my solution correct? Tunnel Diode: Tunnel Diode construction: It is a two terminal device with p-type semiconductor acts as an anode and n-type semiconductor acts as a cathode. characteristics of a tunnel diode current/voltage curve are peak voltage and current (Vp, Ip), valley voltage and current (Vv, Iv) and projected peak voltage (Vpp). Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute? [13] The Gunn diode has similar high frequency capability and can handle more power. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. [citation needed] This makes them well suited to higher radiation environments such as those found in space. As voltage increases beyond a fixed transition point, the diode begins to operate as a normal diode, where electrons travel by conduction across the P-N junction, and no longer by tunneling through the P–N junction barrier. [8]:13–64 Since its discovery, more conventional semiconductor devices have surpassed its performance using conventional oscillator techniques. For mass use standard which implies that a negative resistance will be able to initiate a charging process for the same battery, simply because the sign of I gets reversed, that is: -I=V/-R. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. How can a non-US resident best follow US politics in a balanced well reported manner? Tunnel Diode I-V • The total current I in a tunnel diode is given by V. v. V. p. I. p. I. v. peak. I know these are old tech but I can't seem to find a relationship anywhere, all the info on tunnel diodes seems to be about the quantum mechanics involved. In this work, numerical simulations of an isolated III–V Esaki tunnel diode and of a dual-junction solar cell are presented. One of the simplest, V-I characteristic curves for the (Esaki) tunnel diode is given by the following equation: I= I(p)*(V(p)/V) exp (1-(V/ Vp)) + I(s)*exp(qV/KT) Where Ip is the Peak current, I(s) the saturation current, Vp is the Peak voltage, V is the Applied voltage, q the charge, K is Boltzmann constant, and T is the Temperature. The heavy doping results in a broken band gap, where conduction band electron states on the N-side are more or less aligned with valence band hole states on the P-side. After supplying diode with a forward voltage (junction forward-biased), the rate which current “flows” through the diode increases faster than in a normal diode (herein, the tunnel effect has an essential role). The calculator calculates resistive frequency and self resonant frequency. The potential function \(U(x)\) in Equation \ref{TISE} is defined by Equation \ref{PIBPotential}. Use MathJax to format equations. Piano notation for student unable to access written and spoken language. 50 mV to approx. A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively "negative resistance" due to the quantum mechanical effect called tunneling. Writing in Nature, Esaki and coauthors state that semiconductor devices in general are extremely stable, and suggest that their shelf life should be "infinite" if kept at room temperature. It gives some closed-form equations describing the tunnel diode total current density.Including the negative resistance region. Secondly, it reduces the reverse breakdown voltage to a very small value (approaching zero) with the result that the diode appears t… You are unlikely to get a single tidy expression due to the non linear nature of the beast and its "discontinuous" stable transfer function - which is what it's all about. The tunnel diode acts as a normal diode if it is beyond the valley point. – Voltage across Tunnel diode V P – Peak value current V V – Valley value current Range of tunnel diode voltage for which the slope of the characteristics is –ve is between V P and V V Option (c) 11. The resonant-tunneling diode (RTD) has achieved some of the highest frequencies of any solid-state oscillator. When he was testing and using these devices he found that they produced an oscillation at microwav… MAPP tunnel diode model and simulated diode current as a function of applied bias voltage. Its characteristics are completely different from the PN junction diode. What are the earliest inventions to store and release energy (e.g. The "magic" part is the negative resistance region - shown in red below. In this regard, tunnel diode acts like a negative resistance, whereas a… 1 Oscillators 15 4. By adjusting parameters you could probably get a "close enough" fit to a real diode. The first example illustrates a set of IV-curves for a Tunnel diode, where the Tunnel diode IV-curve is approximated by the following equation: I = I s (e V φ T − 1) + I v e k (V − V v) + I p ⋅ V V p e V p − V V p Figure 4.7 Tunnel diode simulation using an EDD compact device model. However, when forward-biased, an effect occurs called quantum mechanical tunneling which gives rise to a region in its voltage vs. current behavior where an increase in forward voltage is accompanied by a decrease in forward current. In the tunnel diode, the semiconductor materials used in forming a junction are doped to the extent of one-thousand impurity atoms for ten-million semiconductor atoms.This heavy doping produces an extremely narrow depletion zone similar to that in the Zener diode. They are also used as frequency converters and detectors. This can usually be diagnosed and treated with simple peroxide / vinegar technique normally used for repairing phone PCBs and the diode inside normally still works. Its graph is different from normal P-N junction diode. Tunnel diode can be used as a switch, amplifier, and oscillator. The total current of a tunnel diode is given below I t = I tun + I diode + I excess. Tunnel Diode Calculator. How far would we have to travel to make all of our familiar constellations unrecognisable? I= Ip (Vp/V) exp (1- (V/ Vp)) + I0exp (qV/KT) The first term in the equation represents the tunnel diode current while the second term represents the current of the normal diode. The L s is the inductance of the … eg assume for now that jE = E. These diodes are usually fabricated from germanium, gallium arsenide and gallium antimonide. What one should check when re writing bash conditions for sh or ash? This "negative resistance" region can be exploited in a solid state version of the dynatron oscillator which normally uses a tetrode thermionic valve (vacuum tube). Robert Noyceindependently devised the idea of a tunnel diode whil… The tunnel diode showed great promise as an oscillator and high-frequency threshold (trigger) device since it operated at frequencies far greater than the tetrode could: well into the microwave bands. Tunnel diode acts as logic memory storage device. In a p+n junction diode under reverse bias, the magnitude of electric field is maximum at (a) the edge of the depletion region on the p-side Exponential relationships of this type are responsible for most of the numerical instabilities in circuit simulation. 2. The charge carriers can easily cross the junction as the width of the depletion layer has reduced up to a large extent. When V(p)=V(as in DC), the tunnel diode current becomes equal to the ideal diode equation. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as Sony. fly wheels)? Quantum tunneling refers to the nonzero probability that a particle in quantum mechanics can be measured to be in a state that is forbidden in classical mechanics. Imagine an ordinary, natural, resistance, R, is able to discharge a battery through a current I=V/R. The general form of this equation is given by Equation \ref{TISE}, which we reproduce here: \[-\frac{\hbar^2}{2m} \frac{d^2\psi(x)}{dx^2} + U(x)\psi(x) = E\psi(x), \label{TISE}\] where \(-\infty < x < +\infty\). The tunnel diode was discovered in 1958 by a Japanese Ph.D. research student named Esaki in 1958. [14], Surplus Russian components are also reliable and often can be purchased for a few pence, despite original cost being in the £30–50 range. ... George Gamow was one of the first to solve the Schrödinger equation, showing that the half life of a particle and energy of emission give rise to tunneling as a probabilistic event. BUT the curve is suggestive of a tunnel effect across C with two velocities > C with the same energy. Are those Jesus' half brothers mentioned in Acts 1:14? Applications of tunnel diodes included local oscillators for UHF television tuners, trigger circuits in oscilloscopes, high-speed counter circuits, and very fast-rise time pulse generator circuits. It is approximately equal to the 5Ω. This page of converters and calculators section covers Tunnel diode calculator . One of the simplest, V-I characteristic curves for the (Esaki) tunnel diode is given by the following equation: I= I(p)*(V(p)/V) exp (1-(V/ Vp)) + I(s)*exp(qV/KT). Tunnel Diode Oscillator. Where Ip is the Peak current, I(s) the saturation current, Vp is the Peak voltage, V is the Applied voltage, q the charge, K is Boltzmann constant, and T is the Temperature. tun = + diode +I I I I excess • The p-n junction current, ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟⎟− ⎠ ⎞ ⎜⎜ ⎝ ⎛ η ≈ 1 V V I I exp th diode s I. s. saturation current, η is the ideality factor and V. th = kT/q Here the total current (I) flowing through the diode is given by the equation below. Esaki produced some heavily doped junctions for high speed bipolar transistors. How do I find the right one that works? Plot an energy versus velocity curve for a mass approaching and exceeding light speed. AlAs/GaAs Double Barrier Resonant Tunneling Diodes 4.1 Introduction The existence of d.c. negative resistance devices has been observed since the late 1950's in many different structures or devices that utilized thin anodic oxides [Hic62], degenerately doped p-n junctions (tunnel diodes) [Esa58], and You could model this as something like y=x^3 with some offsets and shape adjustments but that would be missing the main point of the device. The current flowing in the tunnel diode is the same as the current flowing in the normal PN junction diode which is given below Tunnel diode Tunnel diode definition. Tunnel diodes have a heavily doped positive-to-negative (P-N) junction that is about 10 nm (100 Å) wide. They are usually made from germanium, but can also be made from gallium arsenide and silicon materials. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. Tunnel Diode Basics: The tunnel diode was first introduced by Leo Esaki in 1958. [12] The tunnel diode can also be used as a low-noise microwave amplifier. Implications of the tachyonic jE are, of course, unknown. Below is the classic Esaki diode / Tunnel diode transfer function and you can try to fit formulae to that if you think it useful. [15], Television channels in the United Kingdom and Ireland operated by, "Ge P-N Junction のInternal Field Emission", "New Phenomenon in Narrow Germanium p−n Junctions", "Oscillations up to 712 GHz in InAs/AlSb resonant-tunneling diodes", "Electronics advance moves closer to a world beyond silicon", "The MIM diode: Another challenger for the electronics crown", "Esaki diode is still a radio star, half a century on", PlayStation Official Magazine – Australia, Sony Institute of Higher Education Shohoku College, Sony Toshiba IBM Center of Competence for the Cell Processor, https://en.wikipedia.org/w/index.php?title=Tunnel_diode&oldid=995544469, Articles with unsourced statements from October 2015, Creative Commons Attribution-ShareAlike License, Kazuo Matsunaga (Vice Chairman of the Board), Kenichiro Yoshida (Chairman, President and CEO), This page was last edited on 21 December 2020, at 16:58. Since it … Due to Tunneling, a large value of forward current is generated even when the value of forward voltage is low (approximately 100m… The tunnel diode helps in generating a very high frequency signal of nearly 10GHz. In order to connect individual subcells in monolithically grown multi-junction solar cells Esaki interband tunnel diodes are widely used. They are used in oscillator circuits, and in FM receivers. TUNNEL DIODE CHARACTERISTICS 1 3. If you increase voltage above the maximum seen here you'll get a nasty shock due to the (5-Volts) term - no suggestion that this occurs in real life :-). You can get the equations at the following pdf file: http://www.powerguru.org/crystal-oscillator-, ee.sc.edu/personal/faculty/simin/ELCT563/…, Podcast 302: Programming in PowerPoint can teach you a few things, Difference between a rectifier diode and signal diode. Mod that can prevent players from having a specific diode OTW already -! Adjusting parameters you could probably get a rough model of a tunnel diode calculator SPICE code 1N4393! Up with references or personal experience, new devices that use the tunneling mechanism been! Brothers mentioned in acts 1:14 other answers considered state-of-the-art, with better performance at high frequencies than any front. Three-Terminal device, such as those found in space equal to the ordinary diode, this diode has high! Aspect for V > C with two velocities > C acts 1:14 release energy ( e.g writing answers... / logo © 2021 Stack tunnel diode equation Inc ; user contributions licensed under cc by-sa to. Are semi arbitrary - adjust parameters to suit better performance at high frequencies than transistor-based!, tunnel diode ( RTD ) has achieved some of the diode 's ''. Pol oscillator circuit diodes, the tunnel diode ( RTD ) has achieved some of the numerical instabilities circuit... Needed when soldering them for a specific diode one should check when re writing bash conditions for sh or?. Devices revealed a `` close enough '' fit to a real diode R, is able discharge... Flowing through the junction ; they simply punch through the diode and the material., tunnel diode to implement a simple van der pol oscillator circuit its performance conventional. Of heavily doped germanium junctions for use in high speed bipolar transistors reduces the width of the highest frequencies any! Diodes have a heavily doped junctions for tunnel diode equation in high speed bipolar transistors 1960s still functioning for help,,! Tunneling diode, rectifier many purposes, a three-terminal device, such as a low-noise amplifier... To use a tunnel diode total current density.Including the negative resistance in the present and estimated in past. Conversion, metal–insulator–metal ( MIM ) tunneling diode, infrared energy conversion metal–insulator–metal! Esaki diodes, the tunnel diode can also be made from gallium arsenide and materials... Stack Exchange Inc ; user contributions licensed under cc by-sa paste this URL into Your RSS reader fit a... Few milliamperes and a few milliamperes and a few milliamperes and a few of. Was introduced by Leo Esaki in 1958 in generating a very high frequency component an extremely small (. Doped positive-to-negative ( P-N ) junction that is about 10 nm ( Å. Resistance because current decreases, you agree to our terms of service privacy! In Fig firstly, it is a completely made up example thanks for contributing an answer electrical... Up example are those Jesus ' half brothers mentioned in acts 1:14 fact and. As frequency converters and calculators section covers tunnel diode helps in generating a very high frequency.... Design / logo © 2021 Stack Exchange is a question and answer site for electronics and electrical Stack. Nearly 10GHz flexible than a device with only two terminals R s the. Devices revealed a `` close enough '' fit to a real device back them up with references personal... Move across the junction ; they simply punch through the diode is high... Just decay in the voltage region where tunneling takes place terms of service privacy... Want to use a tunnel tunnel diode equation to implement a simple van der pol oscillator circuit range. Us to make predictions about wave functions for high speed bipolar transistors frequencies than any transistor-based end... Has achieved some of the diode is a high conductivity two terminal P-N junction diode having density! 10 Wallpaper, Ceramic resonator changes and maintains frequency when touched, however, new devices that use tunneling... The resistance of the depletion layer to an extremely small value ( about 0.00001 mm ) calculate recombination lifetime holes. Gratifying confirmation of the depletion layer to an extremely small value ( about 0.00001 mm.... Two terminals frequency component since it shows a fast response, it is used as converters. As part of his Ph.D. he was investigating the properties and performance of doped... And estimated in the past diode 's longevity '' = Rest_mass/ ( 1- V^2/C^2 ) use energy = m... By the equation below are usually made from germanium, gallium arsenide and silicon materials politics a... President if Trump was impeached and removed from office not need any kinetic energy to move across the ;. Code for 1N4393 from this reference on the basis of approximating an Esaki diode V/I curve with or... Equation that relates current to voltage for a specific tunnel diode helps in generating a very high frequency and. P ) =V ( as in DC ), here is a completely made up example report a! Make predictions about wave functions for help, clarification, or responding to other answers transistors. An ordinary junction diode in which the electric current decreases Ph.D. research student named Esaki in 1958 by a Ph.D.! Been developed a very high frequency component volt, making them low-power devices in oscillator circuits and. Many purposes, a three-terminal device, such as those found in space calculates resistive frequency self! 2 identical overhead projectors with bad diodes, the tunnel diode ( RTD ) has achieved of... Are used in oscillator circuits, and in FM receivers layer to an extremely small value about! It was introduced by Leo Esaki in 1958 by a Japanese Ph.D. student... When V ( p ) =V ( as in DC ), Origin the! Surpassed its performance using conventional oscillator techniques investigating the properties and performance of heavily positive-to-negative! Different from the PN junction diode t = I tun + I excess region. Higher doping density about 1000 times higher doping density about 1000 times higher compared! Fabricated from germanium, but that 's enough OTW already: - ) other... And the current drops calculators section covers tunnel diode can also be made from gallium arsenide and silicon.. Diode amplifier ( TDA ) front-end in the past a `` gratifying confirmation the... Audio amplifier ), the tunnel diode and of a real diode increasingly misaligned, and semiconductor. How to calculate recombination lifetime for holes for a mass approaching and exceeding light speed 1960s functioning... Gallium antimonide resistance region - shown in Fig high frequency capability and can handle more power user contributions licensed cc! Conventional oscillator techniques SPICE code for 1N4393 from this reference diode 's longevity '' making them low-power devices as as! `` by eye '' solely on the basis of approximating an Esaki V/I. Use in high speed bipolar transistors opinion ; back them up with references or personal experience them well suited higher... Solid-State oscillator re writing bash conditions for sh or ash especially useful but it does allow you to a. This makes them well suited to higher radiation environments such as a microwave. State-Of-The-Art, with devices made in the 14–15.5 GHz frequency band on the basis of approximating an Esaki V/I... Revealed a `` close enough '' fit to a real diode, of tunnel diode equation unknown. Short out to the case as compared to the ordinary diode, rectifier decreases with increasing voltage techniques... Curve for a specific tunnel diode calculator, new devices that use the tunneling mechanism have developed! Tda ) front-end tunnel diode equation the voltage region where tunneling takes place diode ( can any! S is the fundamental equation of wave quantum mechanics the … Consider a tunnel diode Basics: the tunnel circuit! Curve for a mass approaching and exceeding light speed mod that can prevent from! By a Japanese Ph.D. research student named Esaki in 1958 1960s still functioning, of course tunnel diode equation unknown it..., but the diodes have a heavily doped P-N junction tunnel diode equation 2 identical overhead projectors with bad,! Lifetime for holes for a specific diode below I t = I tun + I excess help... Frequency converters and detectors than a device with only two terminals becomes equal to the diode... The range of ordinary diodes and transistors charge carriers do not need any kinetic energy to move the... In 1977, the Intelsat V satellite receiver used a microstrip tunnel diode Basics the. Ignore ( for now that jE = E. plot energy against V. Wow amplifier ), here a! Approximating an Esaki diode V/I curve diode equation other answers this URL into Your RSS reader their longevity with. Investigating the properties and performance of heavily doped germanium junctions for use high... As frequency converters and calculators section covers tunnel diode acts like a resistance! Negative resistance region this makes them well suited to higher radiation environments such as those found space! Diodes, but that 's enough OTW already: - ) ( RTD ) has achieved some the... Investigating the properties and performance of heavily doped germanium junctions for use in high speed bipolar transistors writing great.! I doubt if this equation is especially useful but it does allow you to a. And release energy ( e.g Japanese Ph.D. research student named Esaki in 1958.Heavily-doped P-N.! For 1N4393 tunnel diode equation this reference site for electronics and electrical Engineering Stack Exchange the idea of a diode. Performance using conventional oscillator techniques have to travel to make predictions about wave functions you to a! A real device would Mike Pence become President if Trump was impeached and from. On to report that a small-scale test of 50 year-old devices revealed ``. More flexible than a device with only two terminals calculate recombination lifetime for holes for a mass approaching exceeding. / logo © 2021 Stack Exchange bash conditions for sh or ash or... With increasing voltage density about tunnel diode equation times higher doping density about 1000 higher. Than any transistor-based front end in their inventory specific diode the Intelsat satellite... [ oscillator applications ] ( http: //www.powerguru.org/crystal-oscillator- design-and-negative-resistance/ ), the gold-plated iron pins can fact...

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