IEEE Solid-State Circuits Magazine - Summer 2015 - 14
circuit [Figure 3(c)]: M 10 turns M 11
off, M 8 and M 9 disengage C b from
M 11, and M 3 and M 12 precharge C b
to VDD . We observe that each sampling circuit requires at least five
more transistors and one capacitor
for bootstrapping.
Complete Bootstrapped Switch
We now determine the type of
MOSFETs that can be used for the
switches in Figure 3(c). Since M 10
and M 12 connect their respective
drains to ground, they must be realized as NMOS devices. Also, since
M 8 ties the top plate of C b (a high
voltage) to the gate of M 11, it must
use a PMOS transistor. We assume
these three switches are driven by
CK [Figure 4(a)], and hence the circuit enters the hold mode when CK
falls and CK rises.
The choice of M 3 and M 9 entails
interesting points. Precharging the
top plate of C b to VDD, M 3 must be
a PMOS switch, but can we drive its
gate by CK ? In such a case, M 3 must
CK
M3
VDD
be turned off by raising its gate to
VDD, yielding the simplified circuit
of Figure 4(b) in the sampling mode.
Recall that Vp can rise above VDD
because it contains both the precharge voltage and the input swing.
Consequently, as Vp rises, the source
and drain of M 3 exchange roles,
the new source reaches a voltage
exceeding the gate voltage by more
than one threshold, and M 3 turns
on. To avoid this difficulty, we bootstrap the gate of M 3 to Vin as shown
in Figure 4(c).
Transistor M 9 senses the input in
the sampling mode and must therefore be the same type as M 11 . If the
gate voltage of M 9 is at VDD in this
mode, then the transistor turns off or
at least exhibits a large on-resistance
for high values of Vin . We address
this issue by bootstrapping the gate
of this switch as well, arriving at the
topology illustrated in Figure 4(c).
While performing well and providing a high linearity, the sampling circuit of Figure 4(c) entails one
CK
P
M3
Cb
CK
M9
Vout
M11
Vin
VDD
+
VDD
-
Cb
M12
1) In Figure 2(c), R 1 . R 0 . Suppose we
define the small-signal bandwidth
of the sampler as (2rR 0 C 1) -1 . Determine the ratio of ~ in to this
bandwidth if the third-order distortion given by (4) must remain
lower than -60 dB. This example
P
M10
M8
Questions for the Reader
VDD
VDD
X
drawback: when VX rises above VDD
in the sampling mode, M 10 experiences drain-source and drain-gate
voltages greater than VDD . The resulting "stress" shortens the device
lifetime and must be avoided. This
can be accomplished by shielding M 10 through the use of a cascode device [Figure 4(d)] [7]. Now,
M 14 limits VDS10 and VGS10 to about
VDD - VTH14 (when M 10 is off).
The bootstrapping topology studied above has been used in a number
of analog-to-digital converters with
resolutions ranging from 8 b to 12 b
[8], [9]. It has proved to be a robust
solution affording both high linearity and high speed.
Vout
M11
Vin
C1
t
C1
t
(a)
(b)
CK
VDD
CK
CK
VDD
P
M3
CK
M8
X
M12
CK
M11
Vin
M8
M3
M9
Vout
C1
(c)
CK
P
M10
Cb
VDD
X
M10
M14
Cb
M12
M9
Vin
M11
Vout
C1
(d)
Figure 4: (a) A bootstrapping circuit with some switches implemented by MOSFETs, (b) a turn-on issue of M 3, (c) avoiding M 3 turn-on by tying its
gate to X, and (d) the use of M 14 to minimize stress on M 10 .
14
s u m m e r 2 0 15
IEEE SOLID-STATE CIRCUITS MAGAZINE
Table of Contents for the Digital Edition of IEEE Solid-State Circuits Magazine - Summer 2015
IEEE Solid-State Circuits Magazine - Summer 2015 - Cover1
IEEE Solid-State Circuits Magazine - Summer 2015 - Cover2
IEEE Solid-State Circuits Magazine - Summer 2015 - 1
IEEE Solid-State Circuits Magazine - Summer 2015 - 2
IEEE Solid-State Circuits Magazine - Summer 2015 - 3
IEEE Solid-State Circuits Magazine - Summer 2015 - 4
IEEE Solid-State Circuits Magazine - Summer 2015 - 5
IEEE Solid-State Circuits Magazine - Summer 2015 - 6
IEEE Solid-State Circuits Magazine - Summer 2015 - 7
IEEE Solid-State Circuits Magazine - Summer 2015 - 8
IEEE Solid-State Circuits Magazine - Summer 2015 - 9
IEEE Solid-State Circuits Magazine - Summer 2015 - 10
IEEE Solid-State Circuits Magazine - Summer 2015 - 11
IEEE Solid-State Circuits Magazine - Summer 2015 - 12
IEEE Solid-State Circuits Magazine - Summer 2015 - 13
IEEE Solid-State Circuits Magazine - Summer 2015 - 14
IEEE Solid-State Circuits Magazine - Summer 2015 - 15
IEEE Solid-State Circuits Magazine - Summer 2015 - 16
IEEE Solid-State Circuits Magazine - Summer 2015 - 17
IEEE Solid-State Circuits Magazine - Summer 2015 - 18
IEEE Solid-State Circuits Magazine - Summer 2015 - 19
IEEE Solid-State Circuits Magazine - Summer 2015 - 20
IEEE Solid-State Circuits Magazine - Summer 2015 - 21
IEEE Solid-State Circuits Magazine - Summer 2015 - 22
IEEE Solid-State Circuits Magazine - Summer 2015 - 23
IEEE Solid-State Circuits Magazine - Summer 2015 - 24
IEEE Solid-State Circuits Magazine - Summer 2015 - 25
IEEE Solid-State Circuits Magazine - Summer 2015 - 26
IEEE Solid-State Circuits Magazine - Summer 2015 - 27
IEEE Solid-State Circuits Magazine - Summer 2015 - 28
IEEE Solid-State Circuits Magazine - Summer 2015 - 29
IEEE Solid-State Circuits Magazine - Summer 2015 - 30
IEEE Solid-State Circuits Magazine - Summer 2015 - 31
IEEE Solid-State Circuits Magazine - Summer 2015 - 32
IEEE Solid-State Circuits Magazine - Summer 2015 - 33
IEEE Solid-State Circuits Magazine - Summer 2015 - 34
IEEE Solid-State Circuits Magazine - Summer 2015 - 35
IEEE Solid-State Circuits Magazine - Summer 2015 - 36
IEEE Solid-State Circuits Magazine - Summer 2015 - 37
IEEE Solid-State Circuits Magazine - Summer 2015 - 38
IEEE Solid-State Circuits Magazine - Summer 2015 - 39
IEEE Solid-State Circuits Magazine - Summer 2015 - 40
IEEE Solid-State Circuits Magazine - Summer 2015 - 41
IEEE Solid-State Circuits Magazine - Summer 2015 - 42
IEEE Solid-State Circuits Magazine - Summer 2015 - 43
IEEE Solid-State Circuits Magazine - Summer 2015 - 44
IEEE Solid-State Circuits Magazine - Summer 2015 - 45
IEEE Solid-State Circuits Magazine - Summer 2015 - 46
IEEE Solid-State Circuits Magazine - Summer 2015 - 47
IEEE Solid-State Circuits Magazine - Summer 2015 - 48
IEEE Solid-State Circuits Magazine - Summer 2015 - 49
IEEE Solid-State Circuits Magazine - Summer 2015 - 50
IEEE Solid-State Circuits Magazine - Summer 2015 - 51
IEEE Solid-State Circuits Magazine - Summer 2015 - 52
IEEE Solid-State Circuits Magazine - Summer 2015 - 53
IEEE Solid-State Circuits Magazine - Summer 2015 - 54
IEEE Solid-State Circuits Magazine - Summer 2015 - 55
IEEE Solid-State Circuits Magazine - Summer 2015 - 56
IEEE Solid-State Circuits Magazine - Summer 2015 - 57
IEEE Solid-State Circuits Magazine - Summer 2015 - 58
IEEE Solid-State Circuits Magazine - Summer 2015 - 59
IEEE Solid-State Circuits Magazine - Summer 2015 - 60
IEEE Solid-State Circuits Magazine - Summer 2015 - 61
IEEE Solid-State Circuits Magazine - Summer 2015 - 62
IEEE Solid-State Circuits Magazine - Summer 2015 - 63
IEEE Solid-State Circuits Magazine - Summer 2015 - 64
IEEE Solid-State Circuits Magazine - Summer 2015 - 65
IEEE Solid-State Circuits Magazine - Summer 2015 - 66
IEEE Solid-State Circuits Magazine - Summer 2015 - 67
IEEE Solid-State Circuits Magazine - Summer 2015 - 68
IEEE Solid-State Circuits Magazine - Summer 2015 - 69
IEEE Solid-State Circuits Magazine - Summer 2015 - 70
IEEE Solid-State Circuits Magazine - Summer 2015 - 71
IEEE Solid-State Circuits Magazine - Summer 2015 - 72
IEEE Solid-State Circuits Magazine - Summer 2015 - 73
IEEE Solid-State Circuits Magazine - Summer 2015 - 74
IEEE Solid-State Circuits Magazine - Summer 2015 - 75
IEEE Solid-State Circuits Magazine - Summer 2015 - 76
IEEE Solid-State Circuits Magazine - Summer 2015 - 77
IEEE Solid-State Circuits Magazine - Summer 2015 - 78
IEEE Solid-State Circuits Magazine - Summer 2015 - 79
IEEE Solid-State Circuits Magazine - Summer 2015 - 80
IEEE Solid-State Circuits Magazine - Summer 2015 - 81
IEEE Solid-State Circuits Magazine - Summer 2015 - 82
IEEE Solid-State Circuits Magazine - Summer 2015 - 83
IEEE Solid-State Circuits Magazine - Summer 2015 - 84
IEEE Solid-State Circuits Magazine - Summer 2015 - 85
IEEE Solid-State Circuits Magazine - Summer 2015 - 86
IEEE Solid-State Circuits Magazine - Summer 2015 - 87
IEEE Solid-State Circuits Magazine - Summer 2015 - 88
IEEE Solid-State Circuits Magazine - Summer 2015 - Cover3
IEEE Solid-State Circuits Magazine - Summer 2015 - Cover4
https://www.nxtbook.com/nxtbooks/ieee/mssc_fall2023
https://www.nxtbook.com/nxtbooks/ieee/mssc_summer2023
https://www.nxtbook.com/nxtbooks/ieee/mssc_spring2023
https://www.nxtbook.com/nxtbooks/ieee/mssc_winter2023
https://www.nxtbook.com/nxtbooks/ieee/mssc_fall2022
https://www.nxtbook.com/nxtbooks/ieee/mssc_summer2022
https://www.nxtbook.com/nxtbooks/ieee/mssc_spring2022
https://www.nxtbook.com/nxtbooks/ieee/mssc_winter2022
https://www.nxtbook.com/nxtbooks/ieee/mssc_fall2021
https://www.nxtbook.com/nxtbooks/ieee/mssc_summer2021
https://www.nxtbook.com/nxtbooks/ieee/mssc_spring2021
https://www.nxtbook.com/nxtbooks/ieee/mssc_winter2021
https://www.nxtbook.com/nxtbooks/ieee/mssc_fall2020
https://www.nxtbook.com/nxtbooks/ieee/mssc_summer2020
https://www.nxtbook.com/nxtbooks/ieee/mssc_spring2020
https://www.nxtbook.com/nxtbooks/ieee/mssc_winter2020
https://www.nxtbook.com/nxtbooks/ieee/mssc_fall2019
https://www.nxtbook.com/nxtbooks/ieee/mssc_summer2019
https://www.nxtbook.com/nxtbooks/ieee/mssc_2019summer
https://www.nxtbook.com/nxtbooks/ieee/mssc_2019winter
https://www.nxtbook.com/nxtbooks/ieee/mssc_2018fall
https://www.nxtbook.com/nxtbooks/ieee/mssc_2018summer
https://www.nxtbook.com/nxtbooks/ieee/mssc_2018spring
https://www.nxtbook.com/nxtbooks/ieee/mssc_2018winter
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_winter2017
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_fall2017
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_summer2017
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_spring2017
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_winter2016
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_fall2016
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_summer2016
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_spring2016
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_winter2015
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_fall2015
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_summer2015
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_spring2015
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_winter2014
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_fall2014
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_summer2014
https://www.nxtbook.com/nxtbooks/ieee/solidstatecircuits_spring2014
https://www.nxtbookmedia.com