Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-08-08
2001-12-11
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06329870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to reference voltage generating circuitry, and more particularly to reference voltage generating circuitry in an integrated circuit device.
2. Description of the Related Art
In conventional reference voltage generating circuitry, a basic regulated voltage is derived from an unregulated supply, and this basic regulated voltage is then buffered to produce at an output of the circuitry a reference voltage having a desired current driving capability. The basic regulated voltage may be derived, for example, by a reverse-biased Zener diode, or a bandgap reference circuit, and the buffering may be provided by an operational amplifier.
An output impedance of such circuitry typically appears to be inductive, as the gain of the output buffering stage generally falls off with increasing frequency. As shown in
FIG. 1
of the accompanying drawings, the output impedance can be modelled to a reasonable approximation as a fixed inductor. In practice, the actual inductance will not be fixed, but may vary in dependence upon such factors as output current (since the transconductance of an operational amplifier changes with current) and temperature.
Because of the essentially inductive output impedance, the output impedance Z
O
, as seen by load circuitry connected to the output, increases linearly with a frequency &ohgr; of operation of the load circuitry. This does not pose any problems in the case when the generated reference voltage is fed into “static” load circuitry, i.e. load circuitry that has no varying signals, or has signals varying only in a low frequency range where the inductor has very low impedance.
In practice, however, the load circuitry to which the reference voltage generating circuitry is connected may include elements which switch at high frequencies. For example,
FIG. 2
of the accompanying drawings shows an example in which reference voltage generating circuitry
1
, with an inductive output impedance Z
O
, is connected to load circuitry
10
which incorporates switching elements
12
, such as transistors. The load circuitry in this example also includes a constant current sink element
14
. A constant current I is sunk by the current sink element
14
. The effect of the element
14
is to make less significant the changes in the total current drawn by the load circuitry. In this example, the switching elements
12
may be switching currents at a high frequency, for example up to 100 MHz in some applications. This inevitably produces small high-frequency spikes or glitches in the total current drawn from the reference voltage circuitry. At high frequencies the output impedance Z
O
, which is essentially inductive, will be high. Accordingly, any high-frequency variation in current will cause an undesirable corresponding variation in the reference voltage which is delivered from the voltage reference generating circuitry (at node A in FIG.
2
).
In practice, it is desirable that the output impedance of the reference voltage generating circuitry is stable beyond the actual clock frequency applied to the switching elements themselves, as the fast switching times of the switching elements will cause higher-frequency transients to be generated.
In precision applications, for example in high-speed digital-to-analog converters (DACs) or analog-to-digital converters (ADCs) which are clocked at rates of around 100 MHz or more, the variation in reference voltage caused by high-frequency variation in the load circuitry is highly significant.
Accordingly, it is desirable to provide reference voltage generating circuitry capable of generating a reference voltage which is less susceptible to the effects of such high-frequency load variation.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided an integrated circuit device comprising: a load node at which a reference voltage is generated when the device is in use; load circuitry connected to said load node for receiving therefrom said reference voltage; a reference voltage amplifier having an output whose impedance has an effective inductive component in a desired range of operating frequencies of said load circuitry; a first resistance element, having a preselected resistance, connected between said output and said load node for supplying said reference voltage to that node; a connection terminal to which external capacitance having a preselected capacitance is connected when the device is in use; a second resistance element, having a preselected resistance, connected between said load node and said connection terminal; thereby to reduce an impedance variation with frequency of the load node over said desired range of operating frequencies of the load circuitry.
According to a second aspect of the present invention there is provided an integrated circuit device comprising: a plurality of load nodes at which a reference voltage is generated when the device is in use, each said load node having load circuitry connected thereto for receiving said reference voltage therefrom; a reference voltage amplifier having an output whose impedance has an effective inductive component in a desired range of operating frequencies of said load circuitry; and a connection terminal to which external capacitance having a preselected capacitance is connected when the device is in use; said device further comprising, for each said load node: a first resistance element, having a preselected resistance, connected between said output and said load node concerned for supplying said reference voltage to that node; and a second resistance element, having a preselected resistance, connected between said load node concerned and said connection terminal; thereby to reduce an impedance variation with frequency of said plurality of load nodes over said desired range of operating frequencies of the load circuitry.
According to a third aspect of the present invention there is provided an integrated circuit device comprising: a first load node at which a first reference voltage is generated when the device is in use; a second load node at which a second reference voltage is generated when the device is in use; load circuitry connected between said first and second load nodes for receiving therefrom said first and second reference voltages; respective first and second reference voltage amplifiers, each having an output whose impedance has an effective inductive component in a desired range of operating frequencies of said load circuitry; respective first and second connection terminals to which external capacitance having a preselected capacitance is connected when the device is in use; a first resistance element connected between said output of the first reference voltage amplifier and said first load node for supplying said first reference voltage to that node; a second resistance element connected between said first load node and said first connection terminal; a third resistance element connected between said output of said second reference voltage amplifier and said second load node for supplying said second reference voltage to that node; and a fourth resistance element connected between the second load node and said second connection terminal; each of said first to fourth resistance elements having a preselected resistance; thereby to reduce an impedance variation with frequency of the load node over said desired range of operating frequencies of the load circuitry.
According to a fourth aspect of the present invention there is provided an integrated circuit device comprising: a plurality of pairs of load nodes, each pair being made up of a first load node at which a first reference voltage is generated when the device is in use and a second load node at which a second reference voltage is generated when the device is in use, each pair of said plurality having load circuitry connected between said first and second load nodes of that pair for receiving therefrom said first and second reference voltages; respective first and second reference
Fujitsu Limited
Staas & Halsey , LLP
Zweizig Jeffrey
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