Clamped cascode level shifter circuit

Details Clamped cascode level shifter circuit Clamped cascode level shifter circuit

1999-05-20

2001-03-13

Lam, Tuan T. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Amplitude control

C326S062000, C326S080000

Reexamination Certificate

active

06201429

ABSTRACT:

FIELD OF INVENTION
This invention relates to the field of circuit designs, particularly to voltage level shifter circuits.
BACKGROUND OF INVENTION
Level shifter circuits are frequently used to translate one voltage level to another. For example, to conserve power, the “core” voltage within an IC frequently operates at low voltage, but is scaled up at the output. A special class of level shifters is the “half bridge drivers” in which complementary signals are applied to an “upper” and “lower” device. In this application, typically the lower device does not require any special signal processing. The upper device requires level shifting in order to provide adequate Gate-Source enhancement, which is necessary because the source potential is not referenced to ground.
FIG. 1
illustrates a typical half-bridge circuit with a level shifter. Level shifter circuit
10
comprises a first inverter (V
1
)
16
, a pair of control devices
20
and
28
(N
1
and N
2
, respectively), and a cross-coupled pair devices
18
and
24
(P
1
and P
2
, respectively). Complementary signals are applied to N
1
and N
2
which in combination with P
1
and P
2
allow node
26
(Q′) to swing between Vboost
11
and ground. A half-bridge circuit
108
comprising transistors
34
and
38
(N
3
and N
4
, respectively) and a boost circuit is generated by diode
32
(D
1
) in combination with “flying capacitor”
30
(C
1
). A major disadvantage of level shifter circuit
10
is that devices N
1
, N
2
, P
1
and P
2
are all vulnerable to the full voltage excursion from ground to Vboost. This requires special high voltage processing to minimize or avoid the potential of damages to these devices, which adds to manufacturing cost. Furthermore, since the gates of P
1
and P
2
are driven to twice the voltage as N
1
and N
2
, toggling of these devices from one state to another are further aggravated and made more difficult. There is therefore a need for a level shifter circuit that provides the necessary voltage shifting while minimizing the vulnerability of the level shifter to voltage excursions that may damage the circuit devices, as well as improving performance and minimizing difficulties in toggling devices from one state to another.
SUMMARY OF INVENTION
An improved level shifter circuit is provided by toggling a “flying Flip-Flop” comprising a cross-coupled inverter pair with control devices driven out of phase through a pair of cascode transistors. The cross-coupled inverter pair provides pull-up to the positive rail, clamping to a High Side-Common (HSC), and providing Hysteretic Switching. The cascode transistors restrict the pull-down of the control devices, thereby preventing continuous current conduction.


REFERENCES:
patent: 5399920 (1995-03-01), Van Tran
patent: 5502412 (1996-03-01), Choi et al.
patent: 5559464 (1996-09-01), Oril et al.
patent: 5825225 (1998-10-01), Sugisawa et al.
International Rectifier's HEXFET Designer's Manual, Sep. 1993, vol. III, International Rectifier, El Segundo, CA, p. 1652.

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