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does not change very much in octagonal transistors. Therefore, the transistor structure which does not have the influence of STI edge in the channel carriers is effective for reducing the threshold voltage variation. Fig. 11 shows the correlation between VRMS and SS for the rectangular and the octagonal transistors, respectively. SS was extracted at current range of 10-7 A to 10-6 A. Here, the SS of transistors with VRMS higher 90 μV showing RTN signals were plotted. It is clear that pixels where RTN is observed are often found in an area larger than the average SS value indicated by dotted lines in this figure. The obtained result shows that transistors with large SS lead to large VRMS
[8] in rectangular and octagonal transistors. Fig. 12 shows the appearance probability of transistors with RTN, defined by VRMS of more than 90 μV as a function of the segmented SS regions for rectangular and octagonal transistors. Here, the bin size of SS was taken at 2 mV/decade. It is clear that when SS becomes larger, the appearance probability of transistors with large VRMS becomes higher[8]. Comparing these two types of transistors, there are large SS values in rectangular transistors. It shows that the percolation of channel occurs due to the STI edge. Furthermore, the result suggests that the trap density at the STI edge is higher than that at the gate insulator film on main channel because the appearance probability of octagonal transistors is smaller than that of rectangular transistors at the same range of SS. Fig. 13 shows the cross sectional views of the trapezoidal transistors. Comparing (a) with (b), the transistors with narrow gate width at source side induce
higher carrier density at source side than transistors with narrow gate width at drain side under constant drain current operation. For this reason and from the distribution in Fig. 6(c), it is considered that the increase of current density at source side is effective for reducing RTN because the traps near source side are more influential to the RTN appearance probability[7], and higher drain current density operation reduces the effect of the parasitic transistor due to the sub-channel formed by electric field concentration around the STI edge.
CONCLUSION
In this paper, by evaluating the array test circuit with various shapes of SF transistors in pixels of a CMOS image sensor, it was demonstrated that transistor without STI edge is effective for reducing RTN because of the suppression of generating percolated channel around STI edge where the trap density is likely to be high. It was also shown that increasing carrier density at source side of the channel is effective to reduce RTN. These findings are important to the design of in-pixel SF transistors with small RTN for low noise CMOS image sensors.
REFERENCES [1] C. Leyris et al., Proc. ESSCIRC, p. 376, 2006. [2] M. J. Kirton, et al., Adv. Phys. 38, p. 367, 1989. [3] A. Yonezawa, et al., Proc. Int. Rel. Phys. Symp., p. 3B.5.1, 2012. [4] T. Goto, et al., JJAP 54, p.04DA04-1, 2015. [5] D. Pates, et al., ISSCC, Tech. Dig. Papers, p.418, 2011. [6] M.W. Seo, et al., IEEE Trans. ED, 61, 6, p. 2093, 2014. [7] K. Abe, et al., Proc. Int. Rel. Phys. Symp, p.996, 2009. [8] R. Kuroda, et al., IEEE Trans. ED, 60, 10, pp. 3555, 2013.
Drain
Source
STI
Gateinsulator
filmTrap
Si
------- -
Drain
Source
STI
Si
- - - - - -- -
Gateinsulator
film
90 100 110 120 13010-1
100
101
102
Rectangular SF (Pix. 2)Octagonal SF (Pix. 6)
Appe
ranc
e pr
obab
ility
of T
r.w
ith R
TN [%
]
Subthreshold Swing Factor [mV/dec]
90
140
190
240
290
340
90 100 110 120 130 140
Subthreshold Swing Factor [mV/dec]
VRM
S [
V]
90
140
190
240
290
340
90 100 110 120 130 140
VRM
S [
V]
Subthreshold Swing Factor [mV/dec]
Average:109 mV/dec
Rectangular SF(Pix. 2)
VBS= -1.9VIDS=0.1μA
Average:101 mV/dec
Octagonal SF(Pix. 6)
VBS= -1.9VIDS=0.1μA
VBS= -1.9VIDS=0.1μA
bin size= 2mV/dec
Fig. 11. Correlation between VRMS and SS for (a) rectangular transistors (Pix. 2), (b) octagonal transistors (Pix. 6).
Fig. 12. Appearance probability of transistors with RTN as a function of SS.
Fig. 13. Cross sectional views of trapezoidal transistors. (a) Trapezoidal transistor with shorter gate width at source side, (b) Trapezoidal transistor with longer gate width at source side.
(a) (b)
(a) (b)
Impact of Random Telegraph Noise with Various Time Constants and Number of States in CMOS Image Sensors Rihito Kuroda a, Akinobu Teramoto b and Shigetoshi Sugawa a,b
a Graduate School of Engineering, Tohoku University, b New Industry Creation Hatchery Center, Tohoku University
6-6-11-811, Aza-Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, Japan 980-8579 TEL: +81-22-795-4833, FAX: +81-22-795-4834, Email address: [email protected]
ABSTRACT
In this work, the impact of random telegraph noise (RTN) with various time constants and number of states to noise characteristics of CMOS image sensors are summarized based on a statistical measurement and analysis of a large number of MOSFETs. The obtained results suggest that from a trap located relatively away from the gate insulator/Si interface, the trapped carrier is emitted to the floating diffusion (FD) node. Also, an evaluation of RTN using root mean square values tends to underestimate the effect of RTN with large amplitude and relatively long time constants or multiple states. It is proposed that the amplitude of noise should be incorporated during the evaluation.
INTRODUCTION Detection, characterization and reduction of random
telegraph noise (RTN) are critically important in CMOS image sensors (CIS)[1]. A transition of the trap state (filled or empty) of in-pixel source follower (SF) during correlated double (CDS) sampling generates RTN in CIS. RTN induces relatively large noise amplitude at fixed pixels, and the visibility of RTN in captured images is quite significant. Especially for CIS with sub-electron readout noise, RTN becomes a stumbling block to achieve photon-countable sensitivity with all the pixels[2]. By using the array test circuit, we have previously reported statistical analysis of RTN regarding the effects of device structures, process conditions, detailed analysis of time constants and so on[3-8]. The parameters of RTN include amplitude, time constants (time to capture, c and time to emission, e,) and number of states, and these parameters vary significantly among transistors. For example, measurement results of RTN with sampling period of 1μs and sampling time of 600s revealed that the time constants ratio (<c>/<e>) in two-state RTN is distributed for at least nine order of magnitude[6]. Also, various types of multi-state RTN incorporated with multiple number of traps in a transistor have been reported to appear[7]. The effect of RTN during CIS operation may also vary due to the different sets of RTN parameters. For CIS in general, the effect of RTN is evaluated by the measured values of root mean square of pixel output signal after CDS. The effect of RTN with various parameters to the readout noise of CIS has not been fully studied. Recently, an extraction method of characteristic time constants of RTN (s) based on double sampling has been reported to be useful[9]. In this work, we describe the impact of RTN with various time
constants and number of states in CIS operation using CDS in order to clarify the effects of RTN with various parameters and propose an evaluation method thereof. Distribution of time constants and their behavior to gate overdrive voltage are summarized first. Then, using the waveforms obtained by fast and long sampling (1s period for 600s) of MOSFETs with RTN, noise characteristics in CDS operation with various sampling intervals and sampling numbers were analyzed and important findings are summarized.
EXPERIMENTAL SETUP Fig.1 shows the test circuit used in this work to
statistically analyze the RTN characteristics[3-8]. Fig.2 shows the block diagram of measurement system. Fig.3 summarizes the experimental procedure in this work. The array test circuit was fabricated by a 0.22μm technology node CMOS technology. The gate oxide thickness and gate size (width/length) of measured MOSFETs are 5.6nm and 0.28μm/0.22μm, respectively. At first, output signal of 131K MOSFETs were measured by non-CDS frame sampling to extract MOSFETs with RTN waveforms. Then, for randomly selected 721 MOSFETs with RTN, non-CDS continuous sampling was carried
Fig.1 Test circuit to statistically characterize RTN of in-pixel SF.
Test ChipPKG
Amp. ADC
Voltage generator
FPGA
PC
Board Power supply
Low Noise Bias Source
clk.pulses
digital o/p
analog o/p
Probe cardW
afer
(On-wafer type)
(PKG assembled type)
Unit cell
VOUT
Current Source
VREF
VG VD
Horizontal shift register
Verti
cal s
hift
regi
ster Analog
memory
Fig.2 Block diagram of measurement system.
R12
− 43−
R12
out for each MOSFET with 1μs sampling period for 600s and the parameters of RTN were extracted. After that, the CDS waveforms with various time intervals and sampling numbers were constructed from the obtained non-CDS raw data, and the noise parameters such as root mean square of pixel output voltage (Vrms) and maximum RTN amplitude (ΔVRTN) were extracted to be analyzed.
RESULTS AND DISCUSSIONS Fig.4 shows the cumulative probability distribution of
Vrms of 131K MOSFETs with five drain current (ID) conditions measured at the step 1 in Fig.3. RTN waveforms appeared in about 10% of measured MOSFETs. As previously reported, appearance probability of high Vrms due to RTN is reduced by increasing the drain current. It is because the effect of a trap becomes smaller when the number of carriers in channel is larger. Fig.5 shows the ratio of number of RTN states for the measured MOSFETs under non-CDS continuous sampling extracted at the step 4 in Fig.3. About 40% of the measured MOSFETs with RTN in this work exhibited more than two states under the measurement condition. This suggests the impact of multi-state RTN toward CIS noise characteristics should be paid attention. Fig.6 shows the extracted mean time to capture <c> as a function of mean time to emission <e>. They are distributed broadly for at least six orders of magnitude from several micro seconds to several seconds[6]. Fig.7 shows the dependencies of <c> and <e> on the VGS for extracted 35 MOSFETs[5], and Fig.8 shows the energy band diagrams with capture and emission processes to explain the results in Fig.7. In Fig.7(a), <c> decreases exponentially as VGS increases for all of the extracted MOSFETs. When VGS increases, the channel electron density increases exponentially within the measured conditions. Then the capture probability, which is inversely proportional to <c>, increases exponentially[5]. The dependency of <e> on VGS is categorized into three types as shown in Fig.7(b-d). Here, <e> depends on the distance and difference of energy levels between the trap and conduction band of substrate to which the carrier is emitted[4-5]. In Fig.7(b), <e> increases as VGS increases, it is because the potential barrier toward Si increases. In Fig.7(c), <e> does not
change, indicating the trap position is near the interface. The results in Fig.7(d), where <e> decreases as VGS increases, indicate that for a part of MOSFETs with relatively long <e>, i.e., located relatively away from the interface, trapped electrons are emitted to the poly-Si gate electrode side instead of Si channel side. This is especially problematic to CIS aiming for photon-countable sensitivity because the emitted electrons are mixed with signal electrons at the FD node. This may limit the thinning of the gate oxide of SF, which is effective to reduce RTN amplitude due to the gate capacitance increase.
Figs.9-10 show the relationship of Vrms and VRTN between continuous sampling and CDS modes for various numbers of CDS sampling. Vrms has long been employed as index of noise, however RTN with a large VRTN and a long time constant is underestimated for some applications like movie video capturing in low light level or it may be even undetected because of small Vrms. The VRTN is not suppressed by the CDS operation as indicated in Fig.10 if a capture or an emission occurs during the CDS interval. Fig.11 shows the waveforms, histograms and Vrms as a function of CDS interval for specific four samples A~D shown in Figs.9-10.
Fig.3 Experimental procedure in this work. CDS waveform was constructed by measured continuous sampling data.
0 .0 2 .0 4 .0 6 .0-2
0
2
4
6
8
1 0
1 2
1 4
Id=5 .0A
Id= 3 .0A Id=1 .0A Id=0 .3A
-ln(-ln(F(x)))
Id=0 .1A
1 31072 nM O S , W /L=0 .28 /0 .22 m ,V D=2 .5 V , <V BS> = -1 .2 V ,S am pling ra te / tim e= 0 .7 s / 600 s
99 .9999
110
Cum
ulat
ive
Prob
abilit
y(F(
x)) [
%]
V rm s [m V ]
50
90
99
99.9
99 .99
99.999
Sampling period / time= 0.7sec / 600sec
Fig.4 Cumulative probability of Vrms for five ID conditions measured at the step 1 in Fig.3.
Fig.5 Pie chart of the number of RTN states for (a) ID=0.1A and (b) ID=5.0A, respectively.
100 101 102 103 104 105 106 107100
101
102
103
104
105
106
107
0.1 A 0.3 A 1 A 3 A 5 A
<c>
[µse
c]
<e> [µsec]Fig.6 Distribution of measured <e> and <c>. <e> and <c> are broadly distributed for at least six orders of magnitude.
14.4%
12%
13.2%60.4%
Two-statesThree
Four
Five or more
ID = 0.1μA(a)
7.8%8.9%
19.9%63.4%
Two-statesThree
FourFive or
more
ID = 5.0μA(b)
Start
non-CDS frame sampling, 131072 MOSFETsW/L = 0.28/0.22 m, Tox = 5.6nm
Sampling period / time = 0.7 s / 600 sVD=2.5 V, ID=0.1, 0.3, 1, 3, 5 μA, <Vbs>=-1.2 V
Extract MOSFETs with RTN waveform
non-CDS continuous sampling of randomly picked 721 MOSFETs with RTN
Sampling period / time = 1 μs / 600 sVD =2.5 V, ID=0.1, 0.3, 1, 3, 5 μA
Set Vbs=-1.2 V for each MOSFET
Extract RTN parameters: number of states, c, e, s, Vrms
and RTN Amplitude (VRTN)
CDS data construction from step Sampling period / time= 10ms / 500 s
CDS time interval = 1, 2, 3, 5, 7, 10, 15, 20, 30 μs
Extract noise parameters after CDS: Vrms and RTN Amplitude (VRTN)
End
1
2
3
4
5 3
6
− 44−
The characteristics of Vrms as a function of CDS interval are well fitted for two-state RTN cases by the following equation 1[9], which is a function of the time constants and VRTN.
For the sample D which shows multi-state RTN, its VRTN in CDS operation is determined by the direct transition between the most distant states. This cannot be characterized by taking into account the Vrms only. Consequently, for RTN with relatively long time constant as well as with multiple states, the VRTN should be taken into account together with the Vrms for characterization.
CONCLUSIONS The impact of RTN with various time constants and
number of states to noise characteristics of CIS were demonstrated in this work. It is suggested that from a trap located relatively away from the gate insulator/Si interface, the carrier is emitted to the FD node, which is to be mixed with signal photoelectrons. An evaluation of RTN using Vrms values tends to underestimate the effect of RTN with large amplitude and relatively long time constants or multiple states. It is proposed that the amplitude of noise should be incorporated for the evaluation of RTN. These findings are important for characterization and reduction of RTN. The effect of RTN in correlated multiple sampling will be studied based on the framework developed in this work.
REFERENCES [1] X. Wang, M F. Snoeji, P. R. Rao, A. Mierop, A. J.P
Theuwissen, “Random telegraph signal in CMOS image sensor pixels,” IEDM, Tech. Dig., pp.115-118, 2006.
[2] M-W. Seo, S. Kawahito, K. Kagawa, K. Yasutomi, “A 0.27e−rms Read Noise 220-μV/e− Conversion Gain Reset-Gate-Less CMOS Image Sensor With 0.11-μm CIS Process,” IEEE EDL, Vol.36, No.12, pp.1344-1347, 2015.
[3] K. Abe, S. Sugawa, R. Kuroda, S. Watabe, N. Miyamoto, A. Teramoto, T. Ohmi, Y. Kamata, and K. Shibusawa, “Analysis of source follower random telegraph signal using nMOS and pMOS array TEG,” Proc. IISW, pp. 62-65, 2007.
[4] A. Teramoto, F. Fujisawa, K. Abe, S. Sugawa and T. Ohmi, “Statistical Evaluation for Trap Energy Level of RTS Characteristics,” Symp. VLSI Technology, Dig. Tech. Papers, pp.99-100, 2010.
[5] Y. Yonezawa, A. Teramoto, T. Obara, R. Kuroda, S. Sugawa, T. Ohmi, “The Study of Time Constant Analysis in Random Telegraph Noise at the Subthreshold Voltage Region,” Proc. Intl. Reliability Phys. Symp., XT.11.1-6, 2013.
[6] T. Obara, A. Yonezawa, A. Teramoto, R. Kuroda, S. Sugawa, T. Ohmi, “Extraction of time constants ratio over nine orders of magnitude for understanding random telegraph noise in metal-oxide-semiconductor field-effect transistors,” Jpn. J. Appl. Physics, Vol.53, pp.04EC19-1-7, 2014.
[7] T. Obara, A. Teramoto, A. Yonezawa, R. Kuroda, S. Sugawa and T. Ohmi, “Analyzing Correlation between Multiple Traps in RTN Characteristics,” Proc. Intl. Reliability Phys. Symp., 4A.6.1-4A.6.7, 2014.
[8] R. Kuroda, A. Teramoto and S. Sugawa, “Rondom Telegraph Noise Measurement and Analysis based on Arrayed Test Circuit toward High S/N CMOS Image Sensors,” Proc. Intl. Conf. Microelectronic Test Structures, pp.46-51, 2016.
[9] C. Y-P. Chao, H. TU, T. Wu, K-Y. Chou, S-F. Yeh, F-L. Hsueh, “CMOS Image Sensor Random Telegraph Noise Time Constant Extraction From Correlated To Uncorrelated Double Sampling,” J. Electron Device Society, Vol.5, No.1 pp.79-89, 2017.
0.4 0.5 0.6 0.7 0.8100101102103104105106107108 5.03.00.3 1.0
25 MOSFETs
VGS[V]
<e>
[se
c]
<ID> [A]0.1
0.4 0.5 0.6 0.7 0.8100101102103104105106107108
<c>
[se
c]
VGS[V]
35 MOSFETs
5.03.00.3 1.0 <ID> [A]
0.1
0.4 0.5 0.6 0.7 0.8100101102103104105106107108
3 MOSFETs
VGS[V]
<e>
[se
c]
5.03.00.3 1.0 <ID> [A]
0.1
0.4 0.5 0.6 0.7 0.8100101102103104105106107108
7 MOSFETs
VGS[V]
<e>
[se
c]
5.03.00.3 1.0 <ID> [A]
0.1
(a) (b) (c) (d)Fig. 7 (a) <c> and (b-c) <e> as functions of VGS. <c> for all the extracted MOSFETs follow the same dependency on VGS, i.e., <c> decreases exponentially as VGS increases. For <c>, three dependencies were observed; in (b) <c> increases, in (c) <c> does not change and in (d) <c> decreases as VGS increases, respectively.
Poly-Si gate (FD)
SiSiO2 Poly-Si gate (FD)
SiSiO2 Poly-Si gate (FD)
SiSiO2 Poly-Si gate (FD)
SiSiO2
(a) (b) (c) (d)
VGS
Channel e-
<c>
VGS
<e>VGS
<e> sameVGS
<e>
traps
e-
Fig. 8. Energy band diagrams with (a) capture and (b-c) emission processes of electrons due to traps to explain the results shown in Fig.7(a) though (b), respectively.
(1) /exp12
sRTNce
cerms τtV
ττττ
V
(2) ce
ces ττ
τττ
− 45−
Fig.9 Vrms extracted in CDS with 7sec interval and 10ms period as a function of Vrms extracted in continuous sampling for different CDS sampling numbers; (a) 100, (b) 1000, (c) 10000 and (d) 50000. Markers A~D indicate specific four MOSFETs.
Fig.10 VRTN extracted in CDS with 7sec interval and 10ms period as a function of VRTN extracted in continuous sampling for different CDS sampling numbers, (a) 100, (b) 1000, (c) 10000 and (d) 50000. Markers A~D indicates specific four MOSFETs. The VRTN in CDS increases as the sampling number increases and tends to reach the VRTN in continuous samping mode multiplied by squre root of two.
Fig.11 Waveforms and histogram in continuous sampling and CDS, and Vrms as functions of double sampling interval for samples A~D. Sample C exhibits a relatively long s, thus Vrms in CDS becomes relatively small. However, the VRTN is as large as that of continuous sampling mode times square root of two when signal transition occur during the CDS interval.
0.0 1.0 2.0 3.0 4.00.0
1.0
2.0
3.0
4.0
Vrm
s-C
DS
[mV]
Vrms-Continuous [mV]
CDS interval=7sID=5A
# of sampling 50000
0.0 1.0 2.0 3.0 4.00.0
1.0
2.0
3.0
4.0
Vrm
s-C
DS
[mV]
Vrms-Continuous [mV]
CDS interval=7sID=5A
# of sampling 10000
0.0 1.0 2.0 3.0 4.00.0
1.0
2.0
3.0
4.0
Vrm
s-C
DS
[mV]
Vrms-Continuous [mV]
CDS interval=7sID=5A
# of sampling 1000
0.0 1.0 2.0 3.0 4.00.0
1.0
2.0
3.0
4.0
CDS interval=7sID=5A
Vr
ms-
CD
S [m
V]
Vrms-Continuous [mV]
# of sampling 100
A
B
C
D
A
BC
D
A
BC
D
A
BC
D
(a) (b) (c) (d)
xy 2
0.0 5.0 10.0 15.0 20.00.0
5.0
10.0
15.0
20.0
Ampl
itude
-CD
S [m
V]
Amplitude-Continuous [mV]
CDS interval=7sID=5A
# of sampling 50000
0.0 5.0 10.0 15.0 20.00.0
5.0
10.0
15.0
20.0
Ampl
itude
-CD
S [m
V]Amplitude-Continuous [mV]
CDS interval=7sID=5A
# of sampling 10000
0.0 5.0 10.0 15.0 20.00.0
5.0
10.0
15.0
20.0
Ampl
itude
-CD
S [m
V]
Amplitude-Continuous [mV]
CDS interval=7sID=5A
# of sampling 1000
0.0 5.0 10.0 15.0 20.00.0
5.0
10.0
15.0
20.0
Ampl
itude
-CD
S [m
V]
Amplitude-Continuous [mV]
CDS interval=7sID=5A
# of sampling 100
AB
C
D
AB
CD
AB
C
D
AB
C
D
(a) (b) (c) (d)
xy 2
0.0 20.0 40.0 60.0 80.0 100.0
1188
1192
1196
1200
1204
1208 e=556s, c=5253s, s=503s VRTN=12.1mV, Vrms=3.19mV
Out
put v
olta
ge [m
V]
Sampling time [msec]
0 5 10 15 20 25 30 350.0
0.5
1.0
1.5
2.0
2.5
3.0
Vrm
s [m
V]
Double sampling interval [sec]0 5 10 15 20 25 30 35
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Vrm
s [m
V]
Double sampling interval [sec]
Sample A Sample B Sample C Sample D
Con
tinuo
us
sam
plin
g w
avef
orm
CD
S w
avef
orm
(7s
ec in
terv
al)
Con
tinuo
ussa
mpl
ing
hist
ogra
m#
of s
ampl
ing:
6×
108
CD
Shi
stog
ram
7
sec
inte
rval
# of
sam
plin
g: 5×
104
V rm
sve
rsus
CD
S in
terv
al#
of s
ampl
ing:
5×
104
-12.0 -8.0 -4.0 0.0 4.0 8.0 12.0100
101
102
103
104
105
Freq
uenc
y
Output voltage [mV]
1192 1196 1200 1204 1208 1212104
105
106
107
108
109
1010
Freq
uenc
y
Output voltage [mV]
0.0 20.0 40.0 60.0 80.0 100.0-12.0
-8.0
-4.0
0.0
4.0
8.0
12.0VRTN=12.7mV, Vrms=1.58mV
Out
put v
olta
ge [m
V]
Sampling time [sec]
0.0 5.0 10.0 15.0 20.0
1192
1196
1200
1204
1208
1212 e=85s, c=8.0s, s=7.3s VRTN=10.1mV, Vrms=1.58mV
Out
put v
olta
ge [m
V]
Sampling time [msec]
0.0 20.0 40.0 60.0 80.0 100.0-12.0
-8.0
-4.0
0.0
4.0
8.0
12.0VRTN=17.3mV, Vrms=0.43mV
Out
put v
olta
ge [m
V]
Sampling time [sec]
1188 1192 1196 1200 1204 1208104
105
106
107
108
109
1010
Freq
uenc
y
Output voltage [mV]
-12.0 -8.0 -4.0 0.0 4.0 8.0 12.0100
101
102
103
104
105
Freq
uenc
y
Output voltage [mV]
0.0 5.0 10.0 15.0 20.0
1188
1192
1196
1200
1204
1208 e=53s, c=332s, s=45s, VRTN=9.65mV, Vrms=1.97mV
Out
put v
olta
ge [m
V]
Sampling time [msec]
0.0 20.0 40.0 60.0 80.0 100.0-12.0
-8.0
-4.0
0.0
4.0
8.0
12.0
VRTN=12.6mV, Vrms=0.88mV
Out
put v
olta
ge [m
V]
Sampling time [sec]
1188 1192 1196 1200 1204 1208104
105
106
107
108
109
1010
Freq
uenc
y
Output voltage [mV]
-12.0 -8.0 -4.0 0.0 4.0 8.0 12.0100
101
102
103
104
105
Freq
uenc
y
Output voltage [mV]
0 5 10 15 20 25 30 350.0
0.5
1.0
1.5
2.0
2.5
3.0
Vrm
s [m
V]
Double sampling interval [sec]
0.0 1.0 2.0 3.0 4.0 5.01188
1192
1196
1200
1204
1208
1212
VRTN=12.3mV, Vrms=1.88mV
Out
put v
olta
ge [m
V]
Sampling time [msec]
0.0 20.0 40.0 60.0 80.0 100.0-12.0
-8.0
-4.0
0.0
4.0
8.0
12.0VRTN=13.6mV, Vrms=1.55mV
Out
put v
olta
ge [m
V]
Sampling time [sec]
1188 1192 1196 1200 1204 1208 1212103
104
105
106
107
108
109
Freq
uenc
y
Output voltage [mV]
-12.0 -8.0 -4.0 0.0 4.0 8.0 12.010-1
100
101
102
103
104
105
Freq
uenc
y
Output voltage [mV]
0 5 10 15 20 25 30 350.0
0.5
1.0
1.5
2.0
2.5
3.0
Vrm
s [m
V]
Double sampling interval [sec]
Direct transition betw eenmost distant states
Due to direct transitions
Due to direct transitions
Eq.(1)
Four states RTN
− 46−