Missing NDR Region

 Missing NDR Region

Tunnel Diode Load Line Reading Log - Part 2/2

Tunnel Diode Load Line Reading Log - Part 2/2

Microwave semiconductor materials and diodes - Poole and Darwazeh, Microwave Active Circuit Analysis and Design, 2016

11.8 Tunnel diodes

The Tunnel diode is basically a very highly doped pn-junction (around 1019 to 1020 cm−3) that makes use of a quantum mechanical effect called tunneling. This type of diode is also known as an Esaki diode, after the inventor, Leo Esaki, who discovered the effect in 1957, a discovery for which he was awarded the Nobel Prize in Physics in 1973. As a consequence of the very high doping, a tunnel diode will have a very narrow depletion region, typically less than 10 nm.

We will not delve into the physics of tunneling, which is well covered in standard texts. The important point about the tunneling mechanism, from the engineering point of view, is that it gives rise to a region of negative resistance in the I-V characteristics, shown as region “B” in Figure 11.13. 

In region “B,” an increase in forward voltage will result in a decrease in forward current, and vice versa. This is equivalent to saying that the device exhibits negative resistance in this region although, strictly speaking, we should call this negative dynamic resistance, as it refers to the negative slope of the V-I characteristics, not a physical “negative” resistor, which does not exist, of course.

Figure 11.13. Tunnel diode I-V characteristics.

Region “A” in Figure 11.13 is actually the region where tunneling occurs. Region “C” is the region of normal pn-junction behavior. In this sense, region “B” can be considered as the region of transition between region “A,” where the I-V characteristic is linear, and region “C” where the I-V characteristic obeys equation (11.4.5). 

With reference to Figure 11.13 we can see that, as the bias voltage is increased from zero, the current increases linearly along curve “A” until a peak current is reached, at the bias voltage Vp. 

This corresponds to the n-side conduction band becoming aligned with the p-side valance band in the device. 

At this point tunneling stops, at a current level called the peak tunneling current, Ip in Figure 11.13. Ip is also known as the “Esaki current.”

We can analyze the circuit behavior of a tunnel diode with DC bias with the aid of Figure 11.14, from which, by inspection, we can write:

Figure 11.14. Tunnel diode circuit.

(11.8.1)

The current through the diode is then given by:

(11.8.2)

Equation (11.8.2) is in the form of a straight line current/voltage graph with slope (− 1/R) and an intercept on the current axis of (ID = VD/R). This is called a load line. As the voltage across the series combination of resistor plus diode increases, the load line is raised with its x-axis intercept at the applied voltage.

Figure 11.15 shows two possible load lines for the circuit in Figure 11.14, depending on the chosen value of R.

Figure 11.15. Tunnel diode characteristic with a load line.

With higher values of R, the load line will be the shallower load line-1 in Figure 11.15 that intersects the diode characteristic at three points, 1, 2, and 3, meaning that the circuit has three possible operating points. 

Point 2 is an unstable operating point, as any perturbations in bias voltage will cause the diode to jump from point 2 to either point 1 or point 3 on the load line. 

The circuit will therefore settle at either point 1 or point 3 depending on the history. It is in this mode that tunnel diodes are used as switched or memory devices. This mode is of little interest to the microwave circuit designer, however.

If the value of R, is reduced the load line will be much steeper, resembling load line-2 in Figure 11.15. In this case, the circuit has only one operating point, point 4. 

The total differential resistance is negative (because R < |Rd|). In this mode, the diode can be made to oscillate at a microwave frequency dependent on the external L and C components.

Because the negative resistance phenomenon in tunnel diodes relies on a tunneling phenomenon, the currents generated are necessarily quite small and the amount of RF power generated by a tunnel diode oscillator is quite low. 

Consequently, tunnel diodes are only suitable for low power applications and even in this arena they have been largely superseded by transistors.

.END

Tunnel Diode Load Line Reading Log - Part 1/2

Tunnel Diode Load Line Reading Log - Part 1/2

Now I am studying South Carolina University's Online Course EL563 Section 8 Tunnel Diodes.

Part I Tunnel Diode principles Concept of Electron Tunneling (Page 30) 

Background of my Tunnel Diode Blog - Part 2 (Definition of Terms)

 Background of my Tunnel Diode Blog - Part 2 (Definition of Terms)

It is the following EE SE Q&A that aroused my interest in negative resistance and tunnel diode.  I heard about Tunnel Diode long long time ago, but I have never spent time to study the details.

So this time I would like to answer the following questions:

(1)  What is the principle and operation the the tunnel diode?

(2)  What exactly is negative resistance?

(3)  Can we use MOSFET to implement negative resistance?

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References

(1) Differential Resistance vs. R = UI - @Marc, Physics SE, Asked 2018apr17, Viewed 805 times

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Appendix A - EE SE Question on Negative Resistance

Negative resistance from MOSFET circuit - @kepsek, EESE, 2020nov20

From the following IEEE 1979 paper: 

Integrated A-Type Differential Negative Resistance MOSFET DeviceResistance

I'm trying to understand this MOSFET circuit which creates negative resistance. 

Whilst the paper explores how it works, I'm not really understanding it. 

I've tried simulating it in SPICE however I'm not really seeing the negative resistance effect, i.e negative current is proportional to voltage. 

A general overview of this circuit would be greatly appreciated as well as some indication of how to recreate it in LTSpice would be handy.

Equally any more examples of MOSFET based negative resistance would be helpful to understand it deeper. ...

Comments

@tlfong01 Nov 12 

(1) To understand "negative resistance", you must first define it, 

(2) To define something, you must first define the "terms" used, 

(3) For (1) and (2), I would suggest to Wki, 

Negative resistance - Wikipedia 

(4) To test if you do "understand" negative resistance, you should close the "book" and tell me a couple of critical terms/definitions you have just read in the Wiki. For example you might start your list with with the term "differential", and use you own words to define it (with the book closed, :), ... 

(5) Forget the IEEE 1948 paper for now, because you first need to understand the 70 year old terms and conditions used there, which are outdated/obsolete. 

(6) To understand why the three N-FET circuit is dynamically, dfferentially negatively resistive, you need to understand thoroughly the N-FET characteristic and operation, 

(7) Again, after studying the circuit, you must list some critical ideas "between the lines", or more precisely, "among the circuit symbols in the schematic". 

Let me ask you an example question: (a) Why Q1' G and S are shorted? Explain in a couple of sentences pls, ... :) 

.END

PCF8591 Programming - Part 9 (Python program writing three bytes to PCF8591)

PCF8591 Programming - Part 9 (Python program writing three bytes to PCF8591) 

Now I am writing a python program to tell PCF8591 DAC part to output an analog voltage value of half Vcc, ie, 1.66V for Vcc = 3V3.

I using the templet/sketelon's "writeThreeBytesToDevice()" to send three bytes to PCF8591via I2C, using I2C block send command to I2C bus address 0x48.

The three bytes are:

(1) PCF8591 device address byte "0x48", the address of the first PCF8591 device,

(2) PCF8591 control byte, configuring two differential channels, enable analog output etc, 

(3) PCF8591 analog data byte "0x7f", to set analog output top half of Vcc.

PCF8591 Programming - Part 8 (Specification Summary for Programming)

 PCF8591 Programming - Part 8 (Specification Summary for Programming)

PCF8591 Programming - Part 7 (DAC Circuit Analysis)

PCF8591 Programming - Part 7 (DAC Circuit Analysis)

Now I am studying the ADC part of the PCF8591 ADC/DAC module. I am glad to see the reference voltage range and analog ground can be hardware programmed, to setup a floating differential Vt voltage range (0V ~ 0.8V) for powering the tunnel diode.

.END