PROJECT REPORT SHEET
PROJECT DESCRIPTION: Special application diodes
NAME: HYEONGRAE KIM
STUDENT ID: C05723
1. Clippers.
A circuit which removes the peak of a waveform is known as a clipper. A negative clipper
is shown in Figure below. This schematic diagram was produced with Xcircuit schematic
capture program. Xcircuit produced the SPICE net list Figure below, except for the second,
and next to last pair of lines which were inserted with a text editor.
<>
*SPICE 03437.eps
* A K ModelName
D1 0 2 diode
R1 2 1 1.0k
V1 1 0 SIN(0 5 1k)
.model diode d
.tran .05m 3m
.end
Clipper: clips negative peak at -0.7 V.
During the positive half cycle of the 5 V peak input, the diode is reversed biased. The
diode does not conduct. It is as if the diode were not there. The positive half cycle is
unchanged at the output V(2) in Figure below. Since the output positive peaks actually
overlays the input sinewave V(1), the input has been shifted upward in the plot for clarity.
In Nutmeg, the SPICE display module, the command “plot v(1)+1)” accomplishes this.
V(1)+1 is actually V(1), a 5 Vptp sinewave, offset by 1 V for display clarity. V(2) output
is clipped at -0.7 V, by diode D1.
During the negative half cycle of sinewave input of Figure above, the diode is forward
biased, that is, conducting. The negative half cycle of the sinewave is shorted out. The
negative half cycle of V(2) would be clipped at 0 V for an ideal diode. The waveform is
clipped at -0.7 V due to the forward voltage drop of the silicon diode. The spice model
defaults to 0.7 V unless parameters in the model statement specify otherwise.
Germanium or Schottky diodes clip at lower voltages.
Closer examination of the negative clipped peak (Figure above) reveals that it follows the
input for a slight period of time while the sinewave is moving toward -0.7 V. The clipping
action is only effective after the input sinewave exceeds -0.7 V. The diode is not
conducting for the complete half cycle, though, during most of it.
The addition of an anti-parallel diode to the existing diode in Figure above yields the
symmetrical clipper in Figure below.
<>
*SPICE 03438.eps
D1 0 2 diode
D2 2 0 diode
R1 2 1 1.0k
V1 1 0 SIN(0 5 1k)
.model diode d
.tran 0.05m 3m
.end
Symmetrical clipper: Anti-parallel diodes clip both positive and negative peak, leaving a ±
0.7 V output.
Diode D1 clips the negative peak at -0.7 V as before. The additional diode D2 conducts
for positive half cycles of the sine wave as it exceeds 0.7 V, the forward diode drop. The
remainder of the voltage drops across the series resistor. Thus, both peaks of the input
sinewave are clipped in Figure below. The net list is in Figure above
Diode D1 clips at -0.7 V as it conducts during negative peaks. D2 conducts for positive
peaks, clipping at 0.7V.
The most general form of the diode clipper is shown in Figure below. For an ideal diode,
the clipping occurs at the level of the clipping voltage, V1 and V2. However, the voltage
sources have been adjusted to account for the 0.7 V forward drop of the real silicon
diodes. D1 clips at 1.3V +0.7V=2.0V when the diode begins to conduct. D2 clips at -2.3V
-0.7V=-3.0V when D2 conducts.
*SPICE 03439.eps
V1 3 0 1.3
V2 4 0 -2.3
D1 2 3 diode
D2 4 2 diode
R1 2 1 1.0k
V3 1 0 SIN(0 5 1k)
.model diode d
.tran 0.05m 3m
.end
D1 clips the input sinewave at 2V. D2 clips at -3V.
The clipper in Figure above does not have to clip both levels. To clip at one level with one
diode and one voltage source, remove the other diode and source.
The net list is in Figure above. The waveforms in Figure below show the clipping of v(1)
at output v(2).
D1 clips the sinewave at 2V. D2 clips at -3V.
There is also a zener diode clipper circuit in the “Zener diode” section. A zener diode
replaces both the diode and the DC voltage source.
A practical application of a clipper is to prevent an amplified speech signal from
overdriving a radio transmitter in Figure below. Over driving the transmitter generates
spurious radio signals which causes interference with other stations. The clipper is a
protective measure.
Clipper prevents over driving radio transmitter by voice peaks.
A sinewave may be squared up by overdriving a clipper. Another clipper application is the
protection of exposed inputs of integrated circuits. The input of the IC is connected to a
pair of diodes as at node “2” of Figure above . The voltage sources are replaced by the
power supply rails of the IC. For example, CMOS IC's use 0V and +5 V. Analog amplifiers
might use ±12V for the V1 and V2 sources.





REVIEW
A resistor and diode driven by an AC voltage
source clips the signal observed across the diode.
A pair of anti-parallel Si diodes clip symmetrically
at ±0.7V
The grounded end of a clipper diode(s) can be
disconnected and wired to a DC voltage to clip at
an arbitrary level.
A clipper can serve as a protective measure,
preventing a signal from exceeding the clip limits.
2. Clamper.
The circuits in Figure below are known as clampers or DC restorers. The corresponding
netlist is in Figure below. These circuits clamp a peak of a waveform to a specific DC level
compared with a capacitively coupled signal which swings about its average DC level
(usually 0V). If the diode is removed from the clamper, it defaults to a simple coupling
capacitor– no clamping.
What is the clamp voltage? And, which peak gets clamped? In Figure below (a) the clamp
voltage is 0 V ignoring diode drop, (more exactly 0.7 V with Si diode drop). In Figure
below, the positive peak of V(1) is clamped to the 0 V (0.7 V) clamp level. Why is this?
On the first positive half cycle, the diode conducts charging the capacitor left end to +5 V
(4.3 V). This is -5 V (-4.3 V) on the right end at V(1,4). Note the polarity marked on the
capacitor in Figure below (a). The right end of the capacitor is -5 V DC (-4.3 V) with
respect to ground. It also has an AC 5 V peak sinewave coupled across it from source V(4)
to node 1. The sum of the two is a 5 V peak sine riding on a - 5 V DC (-4.3 V) level. The
diode only conducts on successive positive excursions of source V(4) if the peak V(4)
exceeds the charge on the capacitor. This only happens if the charge on the capacitor
drained off due to a load, not shown. The charge on the capacitor is equal to the positive
peak of V(4) (less 0.7 diode drop). The AC riding on the negative end, right end, is
shifted down. The positive peak of the waveform is clamped to 0 V (0.7 V) because the
diode conducts on the positive peak.
Clampers: (a) Positive peak clamped to 0 V. (b) Negative peak clamped to 0 V. (c)
Negative peak clamped to 5 V.
<>
*SPICE 03443.eps
V1 6 0 5
D1 6 3 diode
C1 4 3 1000p
D2 0 2 diode
C2 4 2 1000p
C3 4 1 1000p
D3 1 0 diode
V2 4 0 SIN(0 5 1k)
.model diode d
.tran 0.01m 5m
.end
V(4) source voltage 5 V peak used in all clampers. V(1) clamper output from Figure
above (a). V(1,4) DC voltage on capacitor in Figure (a). V(2) clamper output from Figure
(b). V(3) clamper output from Figure (c).
Suppose the polarity of the diode is reversed as in Figure above (b)? The diode conducts
on the negative peak of source V(4). The negative peak is clamped to 0 V (-0.7 V). See
V(2) in Figure above.
The most general realization of the clamper is shown in Figure above (c) with the diode
connected to a DC reference. The capacitor still charges during the negative peak of the
source. Note that the polarities of the AC source and the DC reference are series aiding.
Thus, the capacitor charges to the sum to the two, 10 V DC (9.3 V). Coupling the 5 V
peak sinewave across the capacitor yields Figure above V(3), the sum of the charge on
the capacitor and the sinewave. The negative peak appears to be clamped to 5 V DC
(4.3V), the value of the DC clamp reference (less diode drop).
Describe the waveform if the DC clamp reference is changed from 5 V to 10 V. The
clamped waveform will shift up. The negative peak will be clamped to 10 V (9.3).
Suppose that the amplitude of the sine wave source is increased from 5 V to 7 V? The
negative peak clamp level will remain unchanged. Though, the amplitude of the sinewave
output will increase.
An application of the clamper circuit is as a “DC restorer” in “composite video” circuitry in
both television transmitters and receivers. An NTSC (US video standard) video signal
“white level” corresponds to minimum (12.5%) transmitted power. The video “black level”
corresponds to a high level (75% of transmitter power. There is a “blacker than black
level” corresponding to 100% transmitted power assigned to synchronization signals. The
NTSC signal contains both video and synchronization pulses. The problem with the
composite video is that its average DC level varies with the scene, dark vs light. The
video itself is supposed to vary. However, the sync must always peak at 100%. To
prevent the sync signals from drifting with changing scenes, a “DC restorer” clamps the
top of the sync pulses to a voltage corresponding to 100% transmitter modulation. [ATCO]




REVIEW:
A capacitively coupled signal alternates about its
average DC level (0 V).
The signal out of a clamper appears the have one
peak clamped to a DC voltage. Example: The
negative peak is clamped to 0 VDC, the waveform
appears to be shifted upward. The polarity of the
diode determines which peak is clamped.
An application of a clamper, or DC restorer, is in
clamping the sync pulses of composite video to a
voltage corresponding to 100% of transmitter
power.
3. Voltage multipliers
FIGURE 4-5 Voltage doublers.
A voltage multiplier provides a dc output voltage that is a multiple of the
circuit’s peak input voltage. For example, a voltage doubler with a peak
input of 10 V provides a dc output that is approximately 20 V. Two voltage
doublers are shown in Figure 4-5.
Each of the circuits in Figure 4-5 provides a dc load voltage that is
approximately twice the value of the peak source voltage. The half-wave
doubler gets its name from the fact that the output capacitor ( ) is
charged during the positive half-cycle of the input signal, as shown in
Figure 4.21. In contrast, the output capacitor in the full-wave doubler ( )
is charged during both alternations of the input cycle, as shown in Figure
4.23. Note that the output from a full-wave doubler has less ripple than the
output from a comparable half-wave doubler.
The voltage tripler is very similar to the half-wave voltage doubler. If you
compare the tripler shown in Figure 4-6 to the circuit in Figure 4-4(a), you
will see that the circuit made up of
,
,
, and
is actually a halfwave voltage doubler. This circuit charges
the negative alternation of the input cycle,
to a value of
. During
is charged to approximately
. The voltage across the series combination of
approximately
combination of
. Since
and
,
and
is
and the load are in parallel with the series
and
are also approximately equal to
.
FIGURE 4-6 A voltage tripler.
The voltage quadrupler contains two half-wave voltage doublers, as shown in
Figure 4-7. The circuit made up of
,
,
, and
charges
to a value
of
. The circuit made up of
of
. The combined charge of
and the load.
,
,
, and
charges
is applied to
to a value
(the filter capacitor)
FIGURE 4-7 A voltage quadrupler.
Voltage multipliers reduce source current by roughly the same factor
that they increase source voltage. For example, a voltage tripler
produces a dc output voltage that is approximately three times the peak
source voltage. At the same time, its maximum output current is roughly
one-third the value of the source current. As such, voltage multipliers
are commonly used in high-voltage, low-current applications. They can
also be used to produce dual-polarity output voltages in power supply
applications (Figure 4.26).
4. Diode circuit troubleshooting
A variety of fault symptom tables are listed in this chapter for clippers, clampers,
multipliers, and displays:





Shunt clipper faults, Table 4.1
Clamper faults, Table 4.2
Additional biased-clamper faults
Additional zener-clamper faults
Voltage multiplier faults Table 4.5
Multisegment displays are often controlled by ICs called decoder-drivers.
These ICs provide the active +V (or ground) inputs required for the
individual segments. The most common multisegment display fault is the
failure of one or more segments to light. When this occurs, check the input
to the common pin. Assuming that the potential there is correct, check the
inputs from the decoder-driver. If the inputs to the display are correct, the
display must be replaced. If not, the decoder-driver (and current-limiting
resistor) must be tested.
5. Varactor diodes
The varactor is a diode that has relatively high junction capacitance when
reverse biased. Varactors are also referred to as varicaps, tuning diodes, and
epicaps. Two commonly used varactor symbols are shown in Figure 5-1a.
(a)
(b)
Figure 5-1. Varactor symbols and capacitance curve.
The magnitude of the reverse voltage across a varactor determines the value of
its junction capacitance. The generic capacitance curve in Figure 5-1b illustrates
the relationship between varactor reverse voltage ( ) and diode capacitance (
). As the curve shows, junction capacitance decreases as the magnitude of
reverse voltage increases. By adjusting the value of
, the value of
can be
set to any value within the component’s rated range. As such, the varactor is
often used as a voltage-controlled capacitor.
Varactors have the same maximum ratings as pn junction and zener diodes. In
addition to these standard ratings, varactor specification sheets typically list the
following capacitance-related ratings:


The diode capacitance temperature coefficient (
) rating indicates the
change in capacitance that occurs per unit change in temperature.
The capacitance ratio ( ) rating indicates the factor by which the
junction capacitance changes from one specified reverse voltage to
another. (This rating is used to determine whether a varactor is best used
in a coarse tuning or a fine tuning circuit.)
Varactors are used almost exclusively in tuned circuits. A tuned circuit that
utilizes a varactor is shown in Figure 5-2. The value of
is adjusted to vary the
amount of reverse bias across the varactor. The reverse bias across the varactor
determines its junction capacitance, and therefore, the resonant frequency of the
circuit. The analysis of a circuit such as the one in Figure 5-2 is demonstrated in
Examples 5.1 and 5.2.
Figure 5-2. A varactor-tuned circuit.
6. Transient suppressors
A transient voltage suppressor or TVS is a general classification of an array of devices
that are designed to react to sudden or momentary overvoltage conditions. One such
common device used for this purpose is known as the transient voltage suppression diode
that is simply a zener diode designed to protect electronics against overvoltages. Another
design alternative applies a family of products that are known as metal-oxide varistor
(MOV) that protect electronic circuits and electrical equipment[1].
The characteristic of a TVS requires that it respond to overvoltages faster than other
common overvoltage protection components such as varistors or gas discharge tubes.
This makes TVS devices or components useful for protection against very fast and often
damaging voltage spikes. These fast overvoltage spikes are present on all distribution
networks and can be caused by either internal or external events, such as lightning or
motor arcing[2].
Applications of transient voltage suppression diodes are used for unidirectional or
bidirectional electrostatic discharge protection of transmission or data lines in electronic
circuits. MOV based TVSs are utilized to protect home electronics, distribution systems
and may accommodate industrial level power distribution disturbances saving downtime
and damage to equipment. The level of energy in a transient overvoltage can be equated
to energy measured in joules or related to amperage when devices are rated for various
applications. These bursts of overvoltage can be measured with specialized electronic
meters that are capable of showing power disturbances of a high amplitude, thousands of
volts, that last for very short time periods, even nanoseconds
7. Constant-current diodes
Constant current diode (also called CLD, current limiting diode, constant-current
diode, diode-connected transistor or current-regulating diode) consists of a JFET
with the gate shorted to the source, and it functions like a two-terminal current limiter or
current source (analog to voltage limiting Zener diode). They allow a current through
them to rise to a certain value, and then level off at a specific value. Unlike zener diodes,
these diodes instead of keeping the voltage constant, keeps the current constant. These
devices keeps the current flowing through them unchanged when the voltage changes.
The maximum limiting voltage ( ) rating for a constant-current diode is the
voltage at which the component begins to regulate current. The peak operating
voltage (POV) is the maximum allowable value of diode forward voltage. The
regulator current ( ) rating is the regulated value of forward current for forward
voltages that are between
and POV.
Constant-current diodes can be used as series current regulators or shunt
current regulators. A series current regulator is illustrated
8. Tunnel diodes
Tunnel Diodes
Part Number
Case
Style
Ip range
(uA)
Tunnel Diode
MP1101
0 - 100
Tunnel Diode
MP1100
0 - 100
Tunnel Diode
MP1102
0 - 100
Tunnel Diode
MP1103
0 - 100
Tunnel Diode
MP1104
0 - 100
Tunnel Diode
MP1105
0 - 100
Tunnel Diode
MP1201
100 - 200
Tunnel Diode
MP1200
100 - 200
Tunnel Diode
MP1202
100 - 200
Tunnel Diode
MP1203
100 - 200
Tunnel Diode
MP1204
100 - 200
Tunnel Diode
MP1205
100 - 200
Tunnel Diode
MP1301
200 - 300
Tunnel Diode
MP1300
200 - 300
Tunnel Diode
MP1302
200 - 300
Tunnel Diode
MP1303
200 - 300
Tunnel Diode
MP1304
200 - 300
Tunnel Diode
MP1305
200 - 300
Tunnel Diode
MP1451
300 - 450
Tunnel Diode
MP1450
300 - 450
Tunnel Diode
MP1452
300 - 450
Tunnel Diode
MP1453
300 - 450
Tunnel Diode
MP1454
300 - 450
Tunnel Diode
MP1455
300 - 450
Tunnel Diode
MP1601
450 - 600
Tunnel Diode
MP1600
450 - 600
Tunnel Diode
MP1602
450 - 600
Tunnel Diode
MP1603
450 - 600
Tunnel Diode
MP1604
450 - 600
Tunnel Diode
MP1605
450 - 600
Typical Detector Circuits
Chip (C2) Assembly Notes
Thermo Compression Wedge Bonding:
1.Use 0.7 mil gold wire.
2.Tip temperature =180°C MAX
3.Stage temperature =160°C MAX
.
Die attach.
1.Silver epoxy with a maximum cure
temperature of 125°C is recommended
Package Assembly Notes
Lead Attach
1.230°C Solder attach for 5 sec. MAX.
CAUTION!
Extremely Static Sensitive Devices
Notes
1.Chip top is cathode.
2. Detected output will be negative
from the cathode contact.
9. Schottky diodes
A Schottky diode is a component that is designed to have very little junction
capacitance. As a result, it is capable of being operated at much higher
frequencies than standard pn junction diodes. The low junction capacitance of
the Schottky diode is a result of its construction. As shown in Figure 5-7, the
anode of the component is constructed using metal in place of a p-type material.
As a result, there is no pn junction, and little junction capacitance.
Figure 5-7. Schottky diode symbol and construction.
PIN Diodes
The PIN diode is a three-layer, two-terminal component that has relatively
constant capacitance when reverse biased. The construction of the PIN diode is
shown in Figure 5-8. The p-type and n-type materials in the PIN diode are heavily
doped, and thus have very little bulk resistance. As a result, the resistance
characteristics of the component (when reverse biased) are very similar to those
of a capacitor.
Figure 5-8. PIN diode construction.
As a result of its construction, the PIN diode:


Begins to conduct in the forward operating region when
exceeds a
minimum threshold value. (In contrast, the pn-junction diode begins
minimal conduction at values of
that are slightly greater than 0 V.)
Does not have an obvious knee (turning point) on its forward operating
curve.
These characteristics are illustrated in Figure 5.24.
PIN diodes are typically used in UHF and microwave applications, most often as
high-speed switches or modulators. A modulator is a circuit (or component) that
combines two signals of different frequencies into a single signal.
10. Step-recovery diodes
The step recovery diode or SRD is a form of semiconductor diode that can be used as a
charge controlled switch and it has the ability to generate very sharp pulses. In view of its
method of operation, it is also called the "Snap-off" diode, "charge storage" diode or
"memory varactor".
The step recovery diode finds a number of applications in microwave radio frequency
electronics as pulse generator or parametric amplifier. It finds uses in a number of
different roles including very short pulse generation, ultra fast waveform generation,
comb generation, and high order frequency multiplication. The step recovery diode is
also capable of working at moderate power levels, and this gives it a distinct advantage
over some other radio frequency technologies that are available.
The step recovery diode, SRD is not as common as many other forms of semiconductor
diode, but it can be very useful in many microwave radio frequency applications.
Step recovery diode structure
The step recovery diode is fabricated with the doping level gradually decreasing as the
junction is approached or as a direct PIN structure. This reduces the switching time
because there are fewer charge carriers in the region of the junction and hence less charge
is stored in this region. This allows the charge stored in this region of the step recovery
diode to be released more rapidly when changing from forward to reverse bias. A further
advantage is that the forward current can also be established more rapidly than in the
ordinary junction diode.
Step recovery diode operation
The step recovery diode is used as what is termed a charge controlled switch. When the
step recovery diode is forward biased and charge enters it, the diode appears as a normal
diode and it behaves in much the same way. When diodes switch from forward
conduction to reverse cut-off, a reverse current flows briefly as stored charge is removed.
When all the charge is removed it suddenly turns off or snaps off. It is the abruptness
with which the reverse current ceases that enables the step recovery diode to be used for
the generation of microwave pulses and also for waveform shaping.
To explain this in more detail, under normal forward bias conditions the diode will
conduct normally. Then if it is quickly reverse biased it will initially appear as a low
impedance, typically less than an ohm. Once the charge that is stored in the device is
depleted, the impedance will very abruptly increase to its normal reverse impedance
which will be very high. This transition occurs very quickly, typically well under a
nanosecond.
This property allows the step recovery diode to be used in pulse shaping (sharpening) and
in pulse generator circuits. The high harmonic content of the signal produced by any
repetitive waveforms from step recovery diode circuits enables them to be used as comb
generators where a comb of harmonically related frequencies are generated.
*****************************End.***************************************