Protection circuit for low voltage devices driven by a high voltage circuit

A method and system for protecting low voltage devices driven by a high voltage circuit is disclosed. The method comprises monitoring an output voltage, from a high voltage block, to a low voltage block. The method further comprises comparing the output voltage with a range of voltages allowable for driving the low voltage block. The range of voltages may be pre-defined or dynamically determined. Furthermore, the method comprises operating a first set of switches and a second set of switches. The first set of switches are operated to feed voltage from the high voltage block to input of the low voltage block, and the second set of switches are operated to feed a plurality of reference voltages to the input of the low voltage block.

PRIORITY CLAIM

The present application claims priority to a provisional application, 2767/CHE/2015, filed on Jun. 2, 2015, entirely of which is attached herewith.

FIELD OF THE INVENTION

The present disclosure relates to a circuit for protecting a low voltage block when driven by a voltage higher than the safe operating voltage.

BACKGROUND

Nowadays, 3G or 4G networks are widely used to support high bandwidths of communication in electronic devices. However, power consumption of the electronic device increases with increase in the bandwidth. As known, the electronic device comprises a plurality of blocks. In order to comply with various specifications related to 3G & 4G standards, the complexity in arranging the plurality of blocks increases.

In electronic devices, such as mobile phones, tablets, laptops, low power consumption is desirable. In order to reduce the power consumption, each block in the electronic device is to be utilized to its fullest capacity. A variety of design techniques such as mixing blocks running on different power supply voltages, sub-threshold design, aggressive power management and various power down modes are used to overcome the difficulty in design and to reduce power consumption.

When the various blocks are running on different power supply voltages, a low voltage block can be driven by a block running on a high voltage power supply to achieve maximum input swing. The power supply voltage of the block driving the low voltage block is higher than the maximum voltage that the low voltage device can sustain without damage. In the example of a mixer, a MOSFET is used as a switch. A switch needs to have low resistance for the maximum transfer of the signal. The resistance of a MOSFET can be reduced by reducing the length. So a low voltage device is used as it can be made to have smaller length. However, the block driving the low voltage device may experience uncontrolled electrical transients, which forces the output of the block to reach as high as the power supply voltage. Further, the block driving the low voltage device may also experience controlled transients, which forces the output voltage to be greater than the maximum safe operating voltage of the low voltage device. The electrical transients generated may damage the low voltage device.

In order to protect the low voltage device, protective devices can be effectively switched into a circuit in response to a transient overvoltage, and subsequently switched out within a reasonably short period to resume normal circuit operation. In prior art, a mixer is arranged to provide a mixed signal by mixing an input signal and an oscillation signal. Usually, the control signal of the mixer switch is the oscillator signal varying over a bias voltage. The input signal is used to bootstrap the oscillator signal. Therefore, the control signal is the oscillator signal varying over the input signal. However, the mixer does not provide protection to the electronic devices during power ON and power OFF and other uncontrolled transients. Further, complexity of the circuitry in the prior art adds additional load to the high frequency clocks.

SUMMARY

The problems in the existing and/or typical systems are met by providing a protection circuit for low voltage devices driven by a high voltage circuit.

An example of a method for protecting low voltage devices driven by a high voltage block, comprises monitoring an output voltage, from a high voltage block to a low voltage block. The method further comprises comparing the output voltage with a range of voltage allowable for driving the low voltage block. Furthermore, the method comprises operating a first set of switches and a second set of switches. The first set of switches are operated when the output voltage is within the range to feed voltage from the high voltage block to input of the low voltage block and the second set of switches are operated when the output voltage is not within the range to feed a plurality of reference voltages to the input of the low voltage block. Further, the range may be pre-defined or dynamically determined. Further, the low voltage block is operated in Radio Frequency (RF) domain and the high voltage block is operated in baseband domain.

An example of a system for protecting low voltage devices driven by a high voltage block comprises a voltage comparator. The voltage comparator monitors an output voltage, from a high voltage block to a low voltage block and compares the output voltage with a range of voltage allowable for driving the low voltage block. The system further comprises a circuit to operate a first set of switches and a second set of switches. The first set of switches are operated when the output voltage is within the range to feed voltage from the high voltage block to input of the low voltage block, and the second set of switches are operated when the output voltage is not within the range to feed a plurality of reference voltages to the input of the low voltage block.

DETAILED DESCRIPTION

In the present disclosure, relational terms such as first and second, and the like, may be used to distinguish one entity from the other, without necessarily implying any actual relationship or order between such entities. The following detailed description is intended to provide example implementations to one of ordinary skill in the art, and is not intended to limit the invention to the explicit disclosure, as one or ordinary skill in the art will understand that variations can be substituted that are within the scope of the invention as described.

The present disclosure describes a protection circuit to protect a low voltage block when driven by a high voltage block. The high voltage block running on a high voltage power supply is used to drive a mixer which contains low voltage devices to obtain maximum swing at the output of the mixer. The protection circuit prevents damage caused to the mixer from the high voltage block by clipping the voltage exceeding a threshold voltage.

FIG. 1illustrates a circuit100for protecting a mixer, in accordance with one embodiment of the present disclosure. The circuit100comprises an input voltage driver block105, a mixer110and a protection circuit115. The input voltage driver block105refers to a block running on a power supply voltage higher than the maximum voltage rating of the mixer110. In other words, the input voltage driver block105is a high voltage block. Further, the input voltage driver block105operates in baseband domain. In one example, the input voltage driver block105is an op-amp based integrating amplifier. Other examples of input voltage driver block include but not limited to power gain amplifiers, filters, analog buffers and DACs. The input voltage driver block105drives a low voltage block. The low voltage block runs at a voltage lower than the supply voltage of the input voltage driver block105. Further, the low voltage block operates in Radio Frequency (RF) domain. In the present embodiment, the low voltage block is the mixer110. The mixer110is one of a voltage mixer and a current-mode mixer. A voltage mode mixer may be one of a passive voltage mixer and an active voltage mixer. The current-mode mixer may be one of a passive current-mode mixer and an active current-mode mixer. Typically, a passive voltage mixer is driven by an analog buffer, configured as a source follower. Although the low voltage block presented in the current embodiment is a mixer110, it should be understood that the low-voltage block may also represent a power amplifier, another buffer, filter etc.

As mentioned above, the input voltage driver block105is a high voltage block. In other words, the input voltage driver block105runs on a voltage V, higher than a maximum voltage rating of the mixer110. For example, consider the input voltage driver block105runs on a 5V supply. The input voltage driver block105drives the mixer110. The mixer110may withstand a maximum voltage, Vmax. In other words, the mixer110may be damaged if a voltage higher than Vmaxis given as input. If there are P type devices in the mixer, then they will get damaged if a voltage lower than a minimum voltage, Vminis given as input. Further, voltage transients from the input voltage driver block105also result in the damage of the mixer110. In order to protect the mixer110, the voltage provided as input should be within a range of voltages allowable for driving the mixer. The range may be pre-defined or dynamically determined by the protection circuit115. In this case, the range may be typically within the minimum voltage, Vminand the maximum voltage, Vmax. In order to ensure the voltage input to the mixer110stays within the range, the protection circuit115generates control signals to operate a plurality of switches. The plurality of switches alter the signal paths to maintain the voltage at the input of the mixer110within the range. In one example the switches are implemented using MOSFETs.

Referring toFIG. 1, the input voltage driver block105drives the mixer110through at least one first switch120. The first switch120is present outside the input voltage driver block105and is operated by a control signal125provided by the protection circuit115. The protection circuit115monitors the output of the input voltage driver block105continuously through a signal130. The input of the mixer110may also be connected to a fixed reference voltage output135of the protection circuit115. The fixed reference voltage output135is connected to the input of the mixer110through at least one second switch140. The operation of the second switch140is controlled by the protection circuit115through a control signal145. In other words, the protection circuit115operates the first switch120and the second switch140through the control signals125and145, generated based on the output from the input voltage driver block105.

The input voltage driver block105supplies an input voltage Vinto the mixer110when the first switch120is closed and when the second switch140is open. For the above, voltage from the output of the input voltage driver block105is directly coupled to the mixer110. The voltage provided as an input to the mixer110is continuously monitored by the protection circuit115. The continuous monitoring of the voltage by the protection circuit115to control and protect the mixer110is explained in the following description.

Consider that the voltage output from the input voltage driver block105goes above a maximum voltage Vmax. The protection circuit115detects an increase in the voltage by sensing the signal130at the input of the mixer110. In response to sensing of increase in voltage, the protection circuit115generates control signals125and145. The control signal125changes to ‘LOW’ state forcing the first switch120to be open. Further, the control signal145in ‘HIGH’ state forces the second switch140to be closed. Consequently, the path of the voltage from the input voltage driver block105is left open and the fixed reference voltage135is fed to the input of the mixer110. In other words, the mixer110is disconnected from the input voltage driver block105and the fixed reference voltage output135of the protection circuit115is connected to the mixer110.

Further, when the signal130reduces to a value within the range i.e., between minimum voltage Vmin, and the maximum voltage Vmax, the protection circuit115generates the control signal125in ‘HIGH’ state and the control signal145in ‘LOW’ state. In other words, the input voltage driver block105is connected back to the mixer110, by closing the first switch120and by opening the second switch140.

The same sequence of steps is followed, if the voltage output from the input voltage driver block105voltage falls below the minimum voltage Vmin. In other words, the mixer110is disconnected from the input voltage driver block105and connected to the fixed reference voltage output135of the protection circuit115. When the voltage returns to the range, i.e., within Vminand Vmax, the mixer110is connected back to the input voltage driver block105.

FIG. 2illustrates a circuit200for protecting a mixer in accordance with another embodiment of the present disclosure. The circuit200comprises an input voltage driver block205, a mixer210and a protection circuit215.

In the present embodiment, the input voltage driver block205is an op-amp based integrating amplifier. The input voltage driver block205drives the mixer210through a first switch220. In the present embodiment, the first switch220is present in the feedback loop, inside the input voltage driver block205. Consequently, the first switch220does not cause distortion. In case of a MOSFET switch, resistance of the switch varies with the gate-to-source voltage, VGS. Therefore, any switch introduced in series with a signal path leads to harmonic distortion of the signal. By putting the switch inside the loop, the distortion caused by the switch is reduced by a factor equivalent to open loop gain Aβ. The first switch220is operated by a control signal225provided by the protection circuit215. The protection circuit215monitors the output of the input voltage driver block205continuously through a signal230. The input of the mixer210may also be connected to a fixed reference voltage output235of the protection circuit215. The fixed reference voltage output235is connected to the input of the mixer210through a second switch240. The protection circuit215controls the operation of the second switch240through a control signal245. The operation of the second switch240is controlled by the protection circuit215through a control signal245. The control of switches by the protection circuit215based on the voltage input to the mixer210is explained in detail usingFIGS. 3 and 4.

FIG. 3illustrates a protection circuit300, in accordance with one embodiment of the present disclosure. Vmaxis the maximum input voltage which may be provided to a mixer (not shown). Any voltage exceeding Vmaxwill damage the mixer. Further, Vminis the minimum input voltage which may be provided to the mixer. Any voltage lower than Vminwill also damage the mixer. In the present embodiment, output from an input voltage driver block302is considered to be a differential voltage. The differential voltage consists of a positive voltage VinPand a negative voltage VinN. The differential voltage from the input voltage driver block302is given as input to the mixer. The protection circuit300monitors the differential voltage supplied to the mixer by the input voltage driver block302. The protection circuit comprises four voltage comparators305,310,315, and320and a logic block325. In the present embodiment, op-amps are used for implementing the voltage comparators. The voltage comparators305,310,315, and320produce respective output by comparing the input voltage from an input voltage driver block302and a reference voltage.

At first, the voltage comparator305within the protection circuit compares the positive voltage, VinPwith Vmax. If VinPexceeds Vmax, then a positive voltage is generated. Similarly, the voltage comparator310compares the negative voltage VinNwith the maximum voltage Vmax. If VinNexceeds Vmax, then a positive voltage is generated. Similarly, the voltage comparators315and320compare the voltages VinPand VinNrespectively with Vmin. The output from the voltage comparators305,310,315, and320are fed to the logic block325. Further, the logic block generates outputs O1, O2, O3, O4, O5, and O6based on the inputs from the voltage comparators305,310,315, and320. The outputs of the logic block O1, O2, O3, O4, O5, and O6are provided to the control of switches (not shown).

FIG. 4illustrates a protection circuit400, in accordance with another embodiment of the present disclosure. Vmaxis the maximum voltage value beyond which the devices in the mixer will be damaged. Vminis the minimum input voltage below which the mixer will be damaged. The protection circuit400comprises four voltage comparators405,410,415, and420and a logic block425. The output of the input voltage driver block402is a differential voltage. The differential voltage consists of a positive voltage VinPand a negative voltage VinN. The voltage comparators405and410compare the positive voltage VinPwith Vmax. Further, the output of the comparators405and410is sent to the input of the logic block425.

The voltage comparators415and420compare the voltages VinPand VinNwith the minimum voltage, Vmin. However, in case of very low values of Vmin, the voltage comparators415and420may require changes in their architecture. In order to use the same voltage comparator architecture as voltage comparators405and410, level shifters430,435and440are used before the voltage comparators415and420, for level shifting Vmin, VinPand VinNrespectively. A level shifted minimum voltage VinNLis compared with a level shifted positive voltage VinPLat the voltage comparator415. Similarly, the level shifted minimum voltage VminLis compared with a level shifted negative voltage VinNLat the voltage comparator420. Further, the output of the comparators415and420is coupled to the input of logic block425. The logic block425generates control signals O1, O2, O3, O4, O5, and O6. The control signals O1, O2, O3, O4, O5, and O6are provided to the control of switches.

FIG. 5illustrates the configuration of a circuit500for protecting low voltage devices in a mixer when driven by a differential voltage, in accordance with one exemplary embodiment of the present disclosure. The circuit500comprises an input voltage driver block510, a first set of switches S1and S2, a second set of switches515,520,525and530, and a mixer535. The input voltage driver block510drives the mixer535through the first set of switches S1and S2. In one example, the first set of switches S1and S2are presented outside the input voltage driver block510. The differential input voltages VinPand VinNare provided across the mixer535. The voltage provided across the mixer535is continuously monitored by a protection circuit (as shown inFIGS. 3 and 4). In one example, control voltages from a logic circuit within the protection circuit are given to the first and second set of switches S1, S2,515,520,525and530. The control signals provided from the protection circuit as discussed inFIGS. 3 and 4control the switches to maintain the input provided to the mixer535within a range, i.e., between minimum voltage Vminand maximum voltage Vmax.

In other words, the protection circuit operates the first set of switches S1, S2and the second set of switches515,520,525and530when the output voltage is not within the range. Specifically, the protection circuit operates the first set of switches S1, S2to feed voltage from input voltage driver block510to input of the mixer535(low voltage block). Further, the protection circuit operates the second set of switches515,520,525and530to feed a plurality of reference voltages to the input of the mixer535(low voltage block). In order to explain working of the protection circuit, an example may be used. Consider the voltage VinPgoes above the maximum voltage Vmax, while the voltage VinNremains within Vminand Vmax. The protection circuit detects the increase in the voltage VinP. In order to maintain the input voltage to the mixer535within the range Vminto Vmax, the protection circuit generates appropriate control signals to operate the first and second set of switches S1, S2,515,520,525and530. In this case, the control signals cause the first switch S1and the second set of switches520,525and530to be open and the first switch S2and the second switch515to be closed. In other words, a reference voltage equal to Vmaxis supplied in place of VinPto the mixer535, when VinPexceeds Vmax. The protection circuit continually monitors the voltages VinPand VinN. When the voltage VinPcomes back to a value with Vminand Vmax, the switch S1is closed and the switch515is opened, to resume normal operation. Similarly, if the voltage VinPgoes below the minimum voltage Vminwhile the voltage VinNremains within Vminand Vmax, then the first switch S2and the second switch520are closed, keeping the first switch S1and the second set of switches515,525and530open. In other words, a reference voltage equal to Vminis supplied in place of VinPto the mixer535, when VinPgoes below Vmin. A similar sequence of steps is performed if the voltage VinNgoes out of the range Vminto Vmax.

In another embodiment, referring toFIG. 5, if VinPgoes above the maximum voltage Vmax, then the second set of switches515and530are closed and the remaining switches are opened, to provide Vmaxand Vminas differential input to the mixer535. Similarly, if VinNgoes below the minimum voltage Vmin, then the second set of switches515and530are closed, to give a differential input of Vmaxand Vminto the mixer535. If VinPgoes below the minimum voltage Vmin, then the second set of switches520and525are closed, to give a differential input of Vminand Vmaxto the mixer535. Similarly, if VinNgoes above the maximum voltage Vmax, then the second set of switches520and525are closed to provide Vminand Vmaxas differential input to the mixer535.

FIG. 6illustrates the configuration of the circuit600for protecting low voltage devices in a mixer when driven by a differential voltage, in accordance with another embodiment of the present disclosure. The circuit600comprises an input voltage driver block610and a mixer635. The input voltage driver block610comprises a first set of switches S1and S2. The circuit600further comprises a second set of switches615,620,625and630. The presence of the a first set of switches S1and S2inside the input voltage driver block610avoids the possibility of harmonic distortion in the output of the mixer635, as would occur if the switches were outside the input voltage driver block610(as inFIG. 5). The differential input voltage VinPand VinNare provided across a mixer635. Control voltages from the protection circuit are given to the first and second set of switches S1, S2,615,620,625and630.

FIG. 7is a flowchart of a method700for protecting a low voltage block driven by an input voltage driver block or a high voltage block, in accordance with one embodiment of the present disclosure. The order in which the method700is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method700or alternate methods. Additionally, individual blocks may be deleted from the method700without departing from the spirit and scope of the disclosure described herein. Furthermore, the method may be implemented in any suitable hardware, software, and combination thereof.

The process begins at step705.

At step710, output voltage of the input voltage driver block is monitored.

At step715, the output voltage is compared with a range of voltages allowable for driving the low voltage block. If the output voltage is within the range, then step720is performed. If the output voltage is outside the range, then step725is performed.

At step720, a first set of switches are operated. The first set of switches are operated to feed voltage from the input voltage driver block to input of the low voltage block,

At step725, a second set of switches are operated to feed a plurality of reference voltages to the input of the low voltage block.

The process ends at step730.

It is to be understood that the method700is a continuous process, whereby the output voltage of the input voltage driver block is monitored continuously (step710) and a first set of switches (step720) and the second set of switches (step725) are operated depending upon the comparison of the output voltage with the range of voltages allowable for driving the low voltage block.

The various implementations of the protection circuit explained above is used to protect any low voltage device driven by a high voltage input. Further, the protection circuit may be used to ensure that the input voltage to the mixer is above a minimum voltage level. Furthermore, the protection circuit may be used in a bootstrap circuit to protect the circuit when the value of input voltage is not known.

In the preceding specification, the present disclosure and its advantages have been described with reference to the specific embodiments. However, it will be apparent to a person with ordinary skill in the art that various modifications and changes can be made, without departing from the scope of the present disclosure, as set forth in the claims below. Accordingly, the specification and figures are to be regarded as illustrative examples of the present disclosure, rather than in restrictive sense. All such possible modifications are intended to be included within the scope of present disclosure.