Input/output cell for integrated circuits

An integrated circuit and method are provided. The integrated circuit comprises: a digital core configured to output a first voltage signal; and a first input/output cell; wherein the first input/output cell is configured to convert the first voltage signal to a first current signal and provide the first current signal to circuitry external to the integrated circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority under 35 U.S.C. § 119 of European Patent application no. 16179764.2, filed on Jul. 15, 2016, the contents of which are incorporated by reference herein.

FIELD

This invention relates to the provision of output signals of a digital integrated circuit and in particular but not exclusively to the provision of those signals under low voltage conditions.

BACKGROUND

Input and output signals from a digital core of an integrated circuit (IC) may be provided externally to the integrated circuit through input/output cells, for example complementary metal oxide semiconductor (CMOS) IO Cells. In some systems, the power supply to the integrated circuit may differ to that of the external circuitry and the CMOS IO cell operates to convert a voltage from the digital core to a voltage in line with the power supply of the external circuitry.

ICs are often tested to check their functionality. As digital cores may be expected to operate under low supply voltage conditions, these conditions may be used to test the operation of the IC. In order for the output of the digital core under these test conditions to be analysed, the CMOS IO cells should also be able to handle the low voltage supply conditions.

Embodiments of the present application aim to address this.

SUMMARY

According to a first aspect, there is provided an integrated circuit comprising: a digital core configured to output a first voltage signal; and a first input/output cell; wherein the first input/output cell is configured to convert the first voltage signal to a first current signal and provide the first current signal to circuitry external to the integrated circuit.

The integrated circuit may further comprise; a second input/output cell configured to convert the first voltage signal to a second voltage signal and provide the second voltage signal to circuitry external to the integrated circuit. The first voltage may correspond to a supply voltage of the integrated circuit and the second voltage corresponds to the supply voltage of the external circuitry. The first current signal may be provided to a first circuit external to the integrated circuit, the first circuit being configured to convert the first current into a third voltage.

The integrated circuit may be in a first voltage domain and the circuitry external to the integrated circuit is in a second voltage domain. The first input/output cell may be configured to operate in low voltage conditions. The first circuit may comprise a transimpedance amplifier.

According to a second aspect, there is provided a method comprising: providing a first output voltage signal from a digital core to a first input/output cell; converting the first voltage signal to a first current signal by the first input/output cell; and providing the first current signal to circuitry external to the integrated circuit.

The method may further comprise: further providing the first voltage output signal to is a second input/output cell; converting the first voltage signal to a second voltage signal by the second input/output cell; and providing the second voltage signal to circuitry external to the integrated circuit. The first voltage may correspond to a supply voltage of the integrated circuit and the second voltage corresponds to the supply voltage of the external circuitry. The method may further comprise: providing the first current signal to a first circuit external to the integrated circuit, the first circuit being configured to convert the first current into a third voltage.

The integrated circuit may be in a first voltage domain and the circuitry external to the integrated circuit is in a second voltage domain. The first input/output cell may be configured to operate in low voltage conditions. The first circuit may comprise a transimpedance amplifier.

According to a third aspect, there is provided a system comprising: the integrated circuit of the first aspect; and a first circuit external to the integrated circuit configured to convert the first current into a voltage; wherein the integrated circuit is in a first voltage domain and the circuitry external to the integrated circuit is in a second voltage domain.

According to a fourth aspect, there is provided an integrated circuit comprising; a digital core; a first input/output cell configured to receive a first current from circuitry external to the integrated circuit, convert the first current to a first voltage to be provided to the digital core.

The integrated circuit may further comprise: a second input/output cell configured to convert receive a second voltage signal from circuitry external to the integrated circuit and convert the second voltage signal to a third voltage signal to be provided to the digital core.

According to a fifth aspect, there is provided a method comprising: receiving by a first input/output cell, a first current signal from circuitry external to an integrated circuit; converting the first current signal to a first voltage signal by the first input/output cell; and providing the first voltage signal to a digital core.

The method may comprise: receiving a second voltage signal at second input/output cell from circuitry external to an integrated circuit; converting the second voltage signal to a third voltage signal by the second input/output cell; and providing the third voltage signal to the digital core.

DETAILED DESCRIPTION

FIG. 1shows an example of a system comprising an integrated circuit having a digital core. The system100comprises an integrated circuit110having a digital core111and a CMOS IO cell112. The integrated circuit is provided with an IC supply voltage113which is coupled to both the digital core111and the IO cell112. It will be appreciated that in some embodiments, the IC supply voltage113may be converted to another voltage before being provided to the IO cell112, however it will be appreciated that the source voltage for the integrated circuit is IC supply voltage113.

The IC110is coupled to further circuitry120via a voltage output130of the IO cell112. The further circuitry is external to the IC110. The external circuitry120may also be CMOS circuitry and may be related to a testing or other functionality of the system100. The external circuitry120may be provided with an external supply voltage121, where is external means external to the IC.

In operation, the digital core may produce an output voltage131and provide this output voltage131to the IO cell112. In one example the output voltage131is a rail-to-rail voltage signal with a maximum amplitude of the IC supply voltage113. The IO cell112receives the voltage signal131from the digital core111and converts it to be compatible with the external voltage supply121. The IC113and the external circuitry120may be in two voltage domains corresponding respectively to the IC supply voltage113and the external supply voltage121. The IO cell112may convert a first voltage signal131in a first voltage domain into a second voltage signal130compatible with the second voltage domain. The second voltage signal130is then provided to the external circuitry.

In some systems, the IO cell112may convert the first voltage131to the second voltage130by level shifting the voltage to be compatible with the external supply voltage121.

In some applications, it may be a requirement that the digital core operates at low voltage conditions. Normal operating conditions can be considered to be a typical voltage +/−10%. The typical voltage may be the ideal voltage under which the digital core was designed to operate, it will be appreciated that this may differ dependent on the application or use of the digital core. Anything less than typical voltage less 10% may be considered to be low voltage conditions. For example, for a typical supply voltage of 1.2V, normal operating conditions can be considered to be between 1.08V to 1.32V. This may be the case where the digital core is designed with a 10% tolerance for supply voltage variation. Low voltage conditions may include conditions where the IC supply voltage113is provided at less than 10% of the operational or typical supply voltage. In this specific above example, low voltage conditions will occur if the digital core receives a voltage less than 1.08V. For example the IC supply voltage may drop to 0.9V or even less depending on what the digital core is expected to handle.

As can be seen fromFIG. 1, the IO cell112is supplied from the IC supply voltage113. When the digital core111is put under low supply condition, the supply to the IO cell112is also lowered during the testing.

Typically, suppliers of IO cells may characterize their products within 10% of the typical supply voltage and are not designed for low supply conditions. When low supply conditions are applied, voltage headroom for the IO cells may become a problem and providing the (digital) voltage signal externally to the IC may become a problem. In particular, voltage level shifter circuits in an IO cell may not be able to cope with low input voltage levels. This may introduce difficulties in the functional and POR (Power-on-Reset) level testing of a digital core under low supply voltage conditions.

Embodiments of the present application may provide IO cell circuitry to convert a voltage output of a digital core to a current. This may aid the ability to provide reliable signal transfer off the IC during low voltage conditions. The IO cell may convert a signal from the digital core from a voltage domain to a current domain which may lead to robustness in terms of low voltage conditions.

FIG. 2shows an example of a system according to an embodiment.

FIG. 2depicts a system200comprising an IC210having a digital core211and an IO ring or block212. The IO ring212comprises a first IO cell213and a second IO cell214. The digital core211and the IO ring212are supplied by a first or IC supply voltage215. Again, it will be appreciated that the supply voltage215may be converted to another voltage before being provided to either of the IO cells213,214or the digital core, however the IC supply voltage215provides the source voltage for the IC210.

The system200further comprises first and second external circuitry230and220. In this example, the external circuitry may be CMOS or other circuitry used for the testing or functional operation of the system200.

Similar to the system100, in operation, the digital core211may produce an output voltage250and provide this output voltage250to the second IO cell214. In one example the output voltage250is a rail-to-rail voltage signal with a maximum amplitude of the IC supply voltage215. The second IO cell214receives the voltage signal250from the digital core211and converts it to be compatible with the external voltage supply240.

The IC210and the external circuitry220,230may be in two voltage domains corresponding respectively to the IC supply voltage215and the external supply voltage240. The second IO cell214may convert a first voltage signal250in a first voltage domain into a second voltage signal251compatible with the second voltage domain. The second voltage signal251is then provided to the external circuitry. The second IO cell214may be a CMOS IO cell and may, for example, provide level shifting to convert the first voltage signal250to the second voltage signal251.

The first voltage signal250from the digital core211may be provided to the first IO cell213. The first IO cell213may convert the first voltage250from a voltage domain to a current domain and provide a current signal252externally to the IC210. In this example the first IO cell213may be a virtual ground input output cell. It will be appreciated that the first IO cell213may operate according to any mechanism to convert the voltage signal to a current signal. For example, the circuitry may be appropriately designed and sized to fit onto the digital core211.

The first IO cell213may be parallel to the second IO cell214. Converting the first voltage signal to a current signal may provide a more reliable transportation of the signal externally to the IC210as the transportation of signals in the current domain may be more robust under low supply voltage conditions. This may be due to the availability of low voltage circuit techniques, inherently used for the VI conversion.

The system200may optionally include first external circuitry230for converting the current signal252back to a voltage signal. In this example, the current signal252may be provided externally to the IC210to the first external circuitry230. The first external circuitry230may, for example, convert the current signal252to a voltage signal. In one example, the first external circuitry230may be a transimpedance amplifier. Conversion back into the voltage domain may be useful in cases where low voltage conditions tests are developed for the voltage domain.

In some examples, output from the first IO cell213may only be taken when the IC210is operating in low voltage conditions. When the IC210is operating under normal operating conditions the output may be taken from the second IO cell214. In other examples, both the first and second IO cells may provide respective outputs251,252under all conditions and external circuitry may select which output to process.

In operation the digital core211may provide a first voltage output250. The first IO cell213may receive the first voltage250and convert it to a current output252. The current output may optionally be received by a first external circuitry230and converted to a third voltage. The digital core211and first and second IO cells213and214may form part of an IC210in a first voltage domain (Vddd). The first external circuitry230may be part of a second voltage domain (Vddext). The first IO cell213and first external circuit230may convert the first voltage250from a voltage in the first digital domain to a third voltage in the second digital domain. The second IO cell214may receive the first voltage250and convert it to a second voltage251suitable for the second digital domain.

The foregoing has exemplified providing signals from a digital core through IO of an IC to be provided off-chip (external to the IC). It will however be appreciated that embodiments may similarly work to receive signals external to the IC and provide them to the digital core. In this case the direction of the arrows inFIG. 2would be reversed.

For example, under normal operating conditions an input voltage251may be provided from external circuitry220to the second IO cell214. The second IO cell214may convert this voltage251to a voltage250to be provided to the digital core. Under low voltage operations, the first external circuitry230may convert a voltage to a current252and provide this current to the first IO cell213. The first IO cell213may convert the current252to a voltage250to be provided to the digital core. It will be appreciated that in some embodiments, the first and second IO cells may operate in both low and normal voltage conditions.

It will be appreciated that embodiments of the present application may be applied in any application where a digital core is to operate or be tested in low voltage conditions and may be provided for any digital application. In a specific example, embodiments may form part of an amplifier, for example an audio amplifier, car radio processing unit or head unit. It will be appreciated however that embodiments may be applied in further applications.