CN115987262A - Low-voltage analog switch circuit - Google Patents
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Abstract
A low voltage analog switch circuit, characterized by: the circuit comprises an analog switch unit, a first substrate control unit and a second substrate control unit, wherein the first substrate control unit and the second substrate control unit are respectively connected with the analog switch unit; the first substrate control unit is used for connecting a substrate of an analog switching tube in the analog switching unit with one end of the analog switching unit so as to reduce the working voltage of the analog switching unit; and the second substrate control unit is used for connecting the substrate of an analog switch tube in the analog switch unit with the bus voltage so as to improve the switch impedance of the analog switch unit. The analog switch circuit has wider application range and can be effectively adapted to circuits with lower driving voltage.
Description
Technical Field
The invention relates to the field of integrated circuits, in particular to a low-voltage analog switch circuit.
Background
In integrated circuit design, CMOS (Complementary Metal Oxide Semiconductor) analog switches are often used for switching paths in various signal transmission processes. The analog switch can realize on-off control through a clock signal, so that an input signal at an input end is periodically led out from an output end.
The analog switch circuit frequently used in the prior art is influenced by the MOS tube substrate bias effect, and the threshold voltage of the analog switch circuit is increased along with the increase of the input end voltage. In order to maintain the normal operation state of the analog switch circuit even when the voltage of the input terminal is high, a high operation voltage needs to be provided for the analog switch circuit to prevent the analog switch circuit from being unable to operate normally. In other words, in order to efficiently drive the operation of the analog switch circuit, the circuit in the related art needs a high operating voltage, and has high power consumption and high requirements for the driving performance of the previous stage circuit.
Therefore, a new low voltage analog switch circuit is needed.
Disclosure of Invention
In order to solve the defects in the prior art, an object of the present invention is to provide a novel analog switch circuit, which realizes the control of the substrate voltage of the switch tube by adding a first substrate control unit and a second substrate control unit under the condition that the switch tube is turned on and off respectively.
The invention adopts the following technical scheme.
A low-voltage analog switch circuit comprises an analog switch unit, a first substrate control unit and a second substrate control unit, wherein the first substrate control unit and the second substrate control unit are respectively connected with the analog switch unit; the first substrate control unit is used for connecting a substrate of an analog switch tube in the analog switch unit with one end of the analog switch unit so as to reduce the working voltage of the analog switch unit; and the second substrate control unit is used for connecting the substrate of the analog switch tube in the analog switch unit with the bus voltage so as to improve the switch impedance of the analog switch unit.
Preferably, when the analog switch unit is turned on, the first substrate control unit is turned on, and the second substrate control unit is turned off; when the analog switch unit is turned off, the first substrate control unit is turned off, and the second substrate control unit is turned on.
Preferably, the first substrate control unit controls the drain electrode of the high-side switching tube Mp1 to be connected with the substrate so that the source-substrate potential difference is greater than 0; or the source electrode of the high-side switching tube Mp1 is controlled to be connected with the substrate, so as to eliminate the substrate bias effect of the high-side switching tube Mp 1.
Preferably, the first substrate control unit controls the source electrode of the low-side switching tube Mn1 to be connected to the substrate, so as to eliminate the substrate bias effect of the low-side switching tube Mn 1; alternatively, the drain of the low-side switching tube Mn1 is controlled to be connected to the substrate so that the source-substrate potential difference is smaller than 0.
Preferably, the first substrate control unit connects the substrate of the analog switch tube in the analog switch unit with the output end of the analog switch unit; when the voltage of the input end of the analog switch unit is higher than the voltage of the output end, the drain electrode of the high-end switch tube Mp1 is connected with the substrate, and the source electrode of the low-end switch tube Mn1 is connected with the substrate; when the voltage at the input end of the analog switch unit is lower than that at the output end, the source electrode of the high-end switch tube Mp1 is connected with the substrate, and the drain electrode of the low-end switch tube Mn1 is connected with the substrate.
Preferably, when the input end voltage of the analog switch unit is higher than the output end voltage, the threshold voltage of the high-end switch tube Mp1 is
The threshold voltage of the low-side switch tube Mn1 is V thnx ＝V th0,n (ii) a Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set; gamma ray p Is the bulk effect coefficient, phi, of the switching tube Mp1 F,p Substrate fermi potential, V, for switching tube Mp1 in For simulating the input voltage, V, of the switching cell out Is the output voltage of the analog switch unit.
Preferably, when the input end voltage of the analog switch unit is lower than the output end voltage, the threshold voltage of the high-end switch tube Mp1 is V thpx ＝V th0,p The threshold voltage of the low-side switching tube Mn1 is
Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set; gamma ray n Is the bulk effect coefficient, phi, of the switching tube Mn1 F,n Substrate fermi potential, V, for switching transistor Mn1 in For simulating the input voltage, V, of the switching cell out Is the output voltage of the analog switch unit.
Preferably, the threshold voltage of the analog switching unit is V thnx +|V thpx |＜V th0,n +|V th0,p L; wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set; v thnx 、V thpx The threshold voltages of the switching tubes Mp1 and Mn1 under the action of the first substrate control unit are respectively.
Preferably, the operating voltage of the analog switch unit is equal to or greater than the threshold voltage V of the analog switch unit thnx +|V thpx |。
Preferably, the first substrate control unit controls the substrate of the high-side switching tube Mp1 to be connected to the working voltage V when the analog switch unit is turned off cc And controlling the substrate of the low-end switch tube Mn1 to be connected to the ground potential.
Preferably, the element of the first and second substrate control units, which controls the connection of the substrate of the analog switch tube in the analog switch unit and the output end of the analog switch unit, is a CMOS transmission gate; the substrate of the analog switch tube in the analog switch unit in the first and second substrate control units is respectively connected with the working voltage V cc The element connected with the ground potential is a switching MOS tube.
Compared with the prior art, the novel analog switch circuit has the advantages that the first substrate control unit and the second substrate control unit are added, the control over the substrate voltage of the switch tube is realized under the condition that the switch tube is turned on and turned off respectively, the threshold voltage of the switch tube is reduced when the switch tube is turned on through the control over the substrate voltage of the MOS tube, and the switching impedance of the switch tube is increased when the switch tube is turned off. Therefore, the analog switch circuit has wider application range and can be effectively adapted to a circuit with lower driving voltage. Meanwhile, the threshold voltage of the switching tube is not increased due to the influence of input and output voltages of the circuit, and the substrate bias effect is effectively overcome.
The beneficial effects of the invention also include:
1. the substrate selection unit only selects one end of the input voltage and one end of the output voltage to be connected, so that the two switching tubes can be ensured to keep the threshold voltage reduced or unchanged under the action of the substrate selection unit no matter which input voltage or output voltage is larger, and the threshold voltage cannot be increased. Therefore, the switching tube which is already opened is completely ensured not to be turned off again under the action of the rising threshold voltage. The time from start-up to stabilization of the circuit is greatly reduced, and meanwhile, a larger range is provided for selection of parameters of each element in each switch tube and substrate selection unit.
2. Compared with the complex situation in the prior art, the invention reduces the use number of the auxiliary switches, and simultaneously obtains the unexpected technical effects of shortening the starting time of the circuit, preventing oscillation, stabilizing the on-resistance, improving the flatness of the on-resistance and the like.
Drawings
Fig. 1 is a schematic diagram of a low voltage analog switch circuit in the prior art;
FIG. 2 is a schematic diagram of another prior art low voltage analog switch circuit;
FIG. 3 is a schematic diagram of a low voltage analog switch circuit according to the present invention;
fig. 4 is a schematic structural diagram of a low-voltage analog switch circuit according to the present invention, in which a MOS transistor analog switch is used to implement a control switch.
Detailed Description
The present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.
Fig. 1 is a schematic structural diagram of a low voltage analog switch circuit in the prior art. As shown in fig. 1, a low-voltage analog switch circuit in the prior art includes a high-side switch transistor Mp1, a low-side switch transistor Mn1, and an inverter Inv1. The high-side switch tube and the low-side switch tube are connected in parallel, and the gates of the high-side switch tube and the low-side switch tube are respectively connected with an enable signal EN and a reverse enable signal EN _ Bar passing through the inverter Inv1. In addition, the substrate of the high-side switching tube Mp1 is connected to the operating voltage Vcc, and the substrate of the low-side switching tube Mn1 is connected to the low level GND.
In addition, after the two switching tubes are connected in parallel, one end of each switching tube is used as the input end of the switching circuit, and the other end of each switching tube is used as the output end of the switching circuit.
In this circuit, the high-side and low-side switching tubes Mp1 and Mn1 are switched between on and off states based on the enable signal and the reverse enable signal, respectively. With the circuit input voltage V in The source-substrate potential difference respectively appearing at the two switching tubes is respectively V in -V cc And V in -0. In this case, according to the calculation formula of the threshold voltage obtained by the switch tube being affected by the substrate bias effect, the threshold voltages of Mp1 and Mn1 can be obtained as shown in the following formulas, respectively.
In this formula, V th0,p 、V th0,n The initial threshold voltages of the switching tubes Mp1 and Mn1 at the source-substrate voltage difference of 0 are respectively. And gamma is p And gamma n Then the bulk effect coefficients, Φ, of Mp1 and Mn1, respectively F,p And phi F,n The fermi potential of the substrate material, respectively, is due to the fact that the above parameters are typically only related to the indices of the metal species, semiconductor conductivity type, doping concentration, temperature, etc. in the CMOS element, and not to other factors. Therefore, after the circuit design is completed and the switch tube type is determined, the four parameters are determined. That is, the threshold voltages of Mp1 and Mn1 in the circuit are determined only by the source-substrate potential difference of the switching tube.
According to the above two formulas, it can be clearly known that when the voltage V at the input end of the circuit is in Range of values from 0V to V cc In between, the induced substrate bias effect causes the threshold voltage of the Mp1 tube and the Mn1 tube to be increased compared with the initial threshold voltage when the substrate bias effect is not existed. Thereby causing an increase in the minimum operating voltage of the circuit.
Fig. 2 is a schematic diagram of another low-voltage analog switch circuit in the prior art. As shown in fig. 2, in another analog switch circuit in the prior art, three auxiliary switches are connected to a main switch Mn4 or Mp4, respectively, wherein the auxiliary switches Mn1 and Mp1 are used to connect the substrate of the main switch and the operating voltage of the main switch, such as Vcc or ground Vss. The two auxiliary switches are switched in through control of the SPG and SNG signals. Specifically, the SPG and SNG signals are inverted and substantially synchronized with the PG and NG signals.
That is, when the PG signal is at a high voltage and the NG signal is at a low voltage, when the main switch in the circuit is turned off, the SPG signal and the SNG signal are at a low level and a high level, respectively, and at this time, the substrate of the Mp4 main switch is connected to the power supply voltage Vdd through the Mp1, so that the substrate voltage of the Mp4 main switch is controlled, and at the same time, mn1 also turns on the connection between the Mn4 main switch and Vss, so that the substrate voltage of Mn4 is reduced to 0V.
Since the PG and NG signals are completely inverted from the SPG and SNG signals, the PG and NG signals cause the other four auxiliary switches, mn2, mn3, mp2 and Mp3, on the main switch to be off. Therefore, the turn-off of the signal makes the main switch not affected by the four switches and performs a normal operation state when turned on.
On the other hand, after the NG and PG signals are level-switched to make the high-low main switching tubes respectively conduct, the circuits Mp1 and Mn1 in the present invention conduct, and Mn2, mn3, mp2 and Mp3 conduct. In the prior art, the sizes of Mn2 and Mn3, and Mp2 and Mp3 are set to the same state, so that when the auxiliary switch tube is conducted, the substrate potential of the main switch can be connected to
(V in/out1 +V in/out2 ) Thereby reducing the substrate bias effect by the voltage difference between the main switch substrate and the source.
It will be appreciated that when the switching circuit is activated, both its input voltage and its output voltage will gradually rise from 0V. Therefore, the substrate voltage of the main switch changes according to the values of the input and output voltages in the process. For Mp4, when Mp4 is turned on, the auxiliary switches Mp2 and Mp3 of Mp4 are also turned on, and at this time, since Mp2 and Mp3 are the same size, the substrate voltage of Mp4 is equal to
(V in/out1 +V in/out2 ). When the source voltage of Mp4 is MAX (V) in/out1 ,V in/out2 ) When the absolute value of the voltage difference between the source of Mp4 and the substrate is ≥ r>
|V in/out1 -V in/out2 L. Due to the substrate bias effect, the switching tube Mp4 is affected by the voltage difference between the substrate and the source, and the threshold voltage at this time changes
This threshold voltage varies with the input voltage and output voltage, and generally decreases whether the input voltage is greater than the output voltage or the output is greater than the input.
However, such circuits still have certain problems. When the switching circuit is started, under the condition that the input and output voltages still do not realize stable change, when the input voltage and the output voltage are lower, the source-drain voltages of Mp4 and Mp2 and Mp3 are both lower, and at this time, although the gate voltage of the MOS transistor is very low, the transistor is turned off because the gate-source voltage difference is very small. When Mp2 and Mp3 are turned off, the substrate of Mp4 is in a floating state, i.e. the substrate of Mp4 is in a high-resistance state. When the Mp4 substrate is in a high impedance state, mp4 is very susceptible to interference, which may come from noise in the supply voltage Vdd or ground potential. When the Mp4 tube is disturbed, the threshold voltage V of the Mp4 tube thp An indeterminate change can occur. If the threshold voltage V is present thp Decreasing may cause Mp4 to turn on earlier. After Mp4 is turned on in advance, at least one of Mp2 and Mp3 is turned on because the gate-source voltage and the threshold voltage of one of Mp2 and Mp3 are completely consistent with Mp4, so that the substrate of Mp4 is restored to a controlled state from a high-resistance state. After the substrate voltage value of the Mp4 is determined, the Mp4 rises again along with the substrate bias effect threshold voltage, which causes the Mp4 tube to be cut off again in the process of slowly rising the input and output voltage. .
It can be seen that, in the process of gradually increasing the voltage at the input terminal of the PMOS switch tube from 0V, multiple switching of on and off may occur along with the change of the threshold voltage, and the on resistance Ron of the whole circuit fluctuates.
On the other hand, the NMOS switch tube has similar problems, and when the input/output voltage across the NMOS switch tube varies under unstable conditions, the voltage difference between the source of Mn4 and the substrate may also vary
Due to the substrate bias effect, the switching tube Mn4 is affected by the voltage difference between the substrate and the source electrode, and the threshold voltage also changes, so that the switching state of the NMOS cannot be stable, and multiple switching occurs between the on state and the off state. The switching not only greatly prolongs the circuit stability time, but also causes the uncertainty of the parameter values such as the on-resistance in the circuit and the like to have the fluctuation of the on-resistance Ron for a long time. Meanwhile, due to the fluctuation of the on-resistance, the value of the flatness (RFLAT, resistor Flat) of the on-resistance is seriously affected, and the value of the threshold voltage of the whole circuit is finally affected.
It can be seen that although this solution can reduce the threshold voltage of the circuit to some extent, there is still a possibility that the threshold voltage of the switching tube is raised, and the time from the turn-on to the steady state of the analog switch is long. It can be found through analysis that the root cause of this problem is that the substrate control circuit of the main switching transistor Mp4 includes only two PMOS transistors, while the substrate control circuit of the main switching transistor Mn4 includes only two NMOS transistors. The threshold voltages of the MOS tubes of the same type are influenced by corresponding parameters in the circuit, and then the change is in the same direction, so that the circuit has the problems.
In order to solve the problem, the analog switch circuit can be suitable for more low-voltage driving circuits and consumes less power, and the invention provides a new technical scheme.
Fig. 3 is a schematic structural diagram of a low voltage analog switch circuit according to the present invention. As shown in fig. 3, a low voltage analog switch circuit, wherein the circuit includes an analog switch unit, a first substrate control unit and a second substrate control unit respectively connected to the analog switch unit; the first substrate control unit is used for connecting a substrate of an analog switch tube in the analog switch unit with one end of the analog switch unit so as to reduce the working voltage of the analog switch unit; and the second substrate control unit is used for connecting the substrate of the analog switch tube in the analog switch unit with the bus voltage so as to improve the switch impedance of the analog switch unit.
It is understood that the analog switch circuit of the present invention, similar to the structure of the analog switch circuit commonly used in the prior art, includes a high-side switch tube Mp1 and a low-side switch tube Mn1. Different from the prior art, the two control units, namely the first substrate control unit and the second substrate control unit, are connected to the high-end switch tube and the low-end switch tube in the invention.
Specifically, the substrate control unit in the invention can realize the connection or disconnection of the switch tube substrate and a plurality of signals at different voltage ends respectively. The working state of the switch tube is controlled by respectively controlling the voltages of the switches Guan Chende. For example, in one aspect, the present invention can reduce or eliminate the substrate bias effect existing on the switching tube through the first substrate control unit, thereby reducing the operating voltage of the switching tube. On the other hand, the invention can enable the switching tube to work in a pinch-off state through the second substrate control unit, thereby improving the on-resistance of the switching tube.
In the present invention, one end of the analog switch unit may be an input end of the analog switch unit, or an output end of the analog switch unit. In the invention, the high-end switch tube and the low-end switch tube in the analog switch unit are completely and symmetrically connected with other parts in the circuit, so that the high-end switch tube and the low-end switch tube can realize different conduction modes under different conditions according to different conditions of the voltage at two ends of the analog switch unit, and therefore, the sources and the drains of the two MOS tubes are not completely determined but are changed at any time according to the specific working condition of the circuit. When the voltage at one end is higher than that at the other end, the high voltage end automatically becomes the input end and the other end becomes the output end. When the voltage changes, the input end and the output end of the circuit are interchanged. Under the premise, the source and the drain of the PMOS tube and the NMOS tube are automatically determined according to the flowing direction of the current between the input end and the output end.
In addition, the BUS voltage refers to the BUS line voltage of the chip or integrated circuit. In the prior art, the substrate of the PMOS transistor is usually connected to a power supply voltage Vcc, which is also referred to as an operating voltage in the present invention, while the substrate of the NMOS transistor is usually connected to a ground potential GND.
The specific principle of the present invention for achieving a reduction of the operating voltage and an increase of the switching impedance by means of the first and second substrate control units will be described later.
Preferably, when the analog switch unit is turned on, the first substrate control unit is turned on, and the second substrate control unit is turned off; when the analog switch unit is turned off, the first substrate control unit is turned off, and the second substrate control unit is turned on.
It is understood that, in the present invention, when the analog switch unit is turned on, the enable signal EN is 0V, and the inverted enable signal EN _ Bar becomes the power voltage Vcc. According to the control of the above two signals, the first substrate control unit in the circuit will be closed, that is, the switches S2 and S3 in fig. 2 will be closed. Specifically, the switch S2 in fig. 2 has one end connected to the output end of the analog switch unit, the other end connected to the substrate of the switch transistor Mp1, and a control end connected to the output end of the inverter, i.e., the inverted enable signal EN _ Bar. The switch S3 and the low-side switching tube Mn1 are connected in a manner similar to that described above.
Meanwhile, when the analog switch unit is turned on, the second substrate control unit is turned off according to the control of the enable signal EN and the reverse enable signal EN _ Bar. That is, switches S1 and S4 in fig. 2 are both in an open state. The switch S1 in fig. 3 has one end connected to the substrate of the switching tube Mp1, the other end connected to the power supply voltage Vcc, and the control end connected to the enable signal EN. Similarly, one end of the switch S4 is connected to the substrate of the switching tube Mn1, and the other end is connected to the ground potential.
On the other hand, when the analog switching unit is switched to the off state, the states of the enable signal EN and the inversion enable signal EN _ Bar are switched, the enable signal becomes the high level Vcc, and the inversion enable signal becomes the low level 0V. At this time, under the control of the enable signal and the reverse enable signal, the states of the first and second substrate control units are changed, the first substrate control unit is opened, and the second substrate control unit is closed. That is, the states of the switches S1 to S4 in fig. 2 all change.
Preferably, the first substrate control unit controls the drain electrode of the high-side switch tube Mp1 to be connected with the substrate, so that the source-substrate potential difference is greater than 0; or the source electrode of the high-side switching tube Mp1 is controlled to be connected with the substrate, so as to eliminate the substrate bias effect of the high-side switching tube Mp 1.
It can be understood that, as described above, the first substrate control unit in the present invention operates only in the on state of the switch tube, and does not affect the circuit in the off state of the switch tube. Therefore, it can be understood that the time interval during which the first substrate control unit controls the circuit is the switch conduction time.
At this time, with the difference of the voltage of the input end and the voltage of the output end in the analog switch unit, the two switch tubes will respectively work in two different states.
First, the present invention is directed to the input terminal voltage V shown in FIG. 3 in Greater than the output voltage V out The conditions of (a) and (b) are described separately.
In one case, for the high-side switching tube Mp1, when the voltage V at the input end is in Greater than output terminal voltage V out In the on state of the PMOS transistor, the current flows from the source to the drain, so that the end of the high-side switch connected to the input terminal automatically becomes the source of the switch, and the other end automatically becomes the drain of the switch. In this case, the voltage connected to the source of the high-side switch tube is the input voltage V in The substrate and drain voltage of the switch tube are both output end voltage V out . At the moment, the source-substrate potential difference of the PMOS tube is V in -V out The potential difference is greater than 0. Substituting the potential difference into a MOS tube threshold voltage calculation formula
In the present case, it can be seen that the threshold voltage of the PMOS transistor is lower than the initial threshold voltage without the body bias effect.
However, there is another case when the voltage V at the input terminal in Less than output voltage V out When in use, the directions of the source electrode and the drain electrode of the PMOS tube are automatically exchanged, at this time, one end of the PMOS tube connected with the input end of the high-end switch tube is the drain electrode of the PMOS tube, and the other end of the PMOS tube is the source electrode. It can be seen that in this case, the drain-connected voltage of the high-side switch tube is the input-side voltage V in The substrate and source voltage of the switch tube are both output end voltage V out . At this time, the source-substrate potential difference of the PMOS tube is 0. Therefore, the PMOS tube does not generate substrate bias effect, and the threshold voltage of Mp1 is equal to the initial threshold voltage at the moment, and has V thpx ＝V th0,p 。
Preferably, the first substrate control unit controls the source electrode of the low-side switching tube Mn1 to be connected with the substrate, so as to eliminate the substrate bias effect of the low-side switching tube Mn 1; alternatively, the drain of the low-side switching tube Mn1 is controlled to be connected to the substrate so that the source-substrate potential difference is smaller than 0.
Concurrent with the first case of the PMOS transistor is when the input terminal voltage V is in Greater than the output voltage V out In the case of the low-side switch tube Mn1, the source of Mn1 is connected to the output terminal voltage of the analog switch circuit, and the sum of the low-side switch tube Mn1 and the substrate is the output terminal voltageV out And the drain electrode of Mn1 is connected with the voltage of the input end. In this case, the source and the substrate of the NMOS transistor are short-circuited and do not have a source-substrate potential difference, so that the NMOS transistor does not have a substrate bias effect, and the threshold voltage of Mn1 at this time is equal to the initial threshold voltage and has V thnx ＝V th0,n 。
In parallel with the other case of PMOS transistor, when the voltage V at the input terminal is in Less than output voltage V out In the case of the low-side switching tube Mn1, the drain of Mn1 is connected to the output voltage of the analog switching circuit, and the source of Mn1 is connected to the input voltage. At this time, the source-substrate potential difference of the NMOS tube is V in Vout, the potential difference being less than 0. Substituting the potential difference into a MOS tube threshold voltage calculation formula
In the present case, it can be seen that the threshold voltage of the NMOS transistor is lower than the initial threshold voltage in the absence of the body bias effect.
The substrate selection unit only selects one end of the input voltage and one end of the output voltage to be connected, so that the two switching tubes can be ensured to keep the threshold voltage reduced or unchanged under the action of the substrate selection unit no matter which input voltage or output voltage is larger, and the threshold voltage cannot be increased. Therefore, the switching tube which is already opened is completely ensured not to be turned off again under the action of the rising threshold voltage. The time from starting to stabilizing of the circuit is greatly reduced, and meanwhile, a larger range is provided for selection of parameters of each element in each switch tube and substrate selection unit.
Preferably, the first substrate control unit connects the substrate of the analog switch tube in the analog switch unit with the output end of the analog switch unit; when the voltage of the input end of the analog switch unit is higher than the voltage of the output end, the drain electrode of the high-end switch tube Mp1 is connected with the substrate, and the source electrode of the low-end switch tube Mn1 is connected with the substrate; when the voltage of the input end of the analog switch unit is lower than that of the output end, the source electrode of the high-end switch tube Mp1 is connected with the substrate, and the drain electrode of the low-end switch tube Mn1 is connected with the substrate.
It is understood that the first substrate control unit of the present invention can select one end of the analog switch unit to connect, and in an embodiment of the present invention, the connection with the output terminal is implemented. In this implementation, as described above, the source and the drain of the switching transistor automatically exchange with each other according to the magnitude of the input voltage and the magnitude of the output voltage, and the direction of the source-drain current flowing through the MOS transistor changes accordingly.
Preferably, when the input end voltage of the analog switch unit is higher than the output end voltage, the threshold voltage of the high-end switch tube Mp1 is
The threshold voltage of the low-end switch tube Mn1 is V thnx ＝V th0,n (ii) a Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set; gamma ray p Is the bulk effect coefficient, phi, of the switching tube Mp1 F,p Substrate fermi potential, V, for switching tube Mp1 in For simulating the input voltage, V, of the switching cell out Is the output voltage of the analog switch unit.
It can be understood that, in the present invention, the threshold voltage is substituted into the calculation formula to obtain that the values of the two MOS transistors are respectively reduced or unchanged relative to the initial threshold voltage.
Preferably, when the voltage at the input end of the analog switch unit is lower than that at the output end, the threshold voltage of the high-end switch tube Mp1 is V thpx ＝V th0,p The threshold voltage of the low-side switching tube Mn1 is
γ n Is the bulk effect coefficient, phi, of the switching tube Mn1 F,n Is a switch tube MSubstrate fermi potential of n1.
In the second operation, the operating states of the two MOS transistors are changed, but the threshold voltages are unchanged from the initial voltages, and the other is reduced.
Preferably, the threshold voltage of the analog switching cell is V thnx +|V thpx |＜V th0,n +|V th0,p L, |; wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set; v thnx 、V thpx The threshold voltages of the switching tubes Mp1 and Mn1 under the action of the first substrate control unit are respectively.
As indicated above, the threshold voltage of the analog switch cell is in both cases smaller than the sum of the initial threshold voltages in the same direction.
Preferably, the operating voltage of the analog switch unit is equal to or greater than the threshold voltage V of the analog switch unit thpx +|V thpx |。
In order to enable the analog switch unit to work normally, the power supply voltage loaded in the circuit should be able to sum up in the same direction over the threshold voltages of the two switching tubes at a minimum. In the invention, the magnitude of the two threshold voltages is summed in the same direction to obtain the working voltage, namely the minimum feasible value of the power supply voltage is V thpx +|V thpx L. the method is used for the preparation of the medicament. Since the two data mentioned above are reduced one and unchanged one, the minimum value of the available supply voltage is effectively reduced.
The operating state of the circuit when the first substrate control unit is closed and the second substrate control unit is open is explained in detail above. It should be noted that, in the case where the analog switch circuit in the circuit is in the off state, the circuit also provides a state where the second substrate control unit performs an operation in order to achieve an effective off.
Preferably, the first substrate control unit controls the substrate of the high-side switching tube Mp1 to be connected to the working voltage V when the analog switch unit is turned off cc And controlling low-end switchAnd the substrate of the switch tube Mn1 is connected to the ground potential.
It will be appreciated that when the first substrate control unit is open, both switches S2 and S3 are open, while both switches S1 and S4 are closed. In this case, the source or the drain of the switch tube in the circuit is no longer connected to the substrate of the switch tube. Meanwhile, the substrate of the PMOS tube is connected with a power supply voltage Vcc. At this time, the voltage of the enable signal is also Vcc, so that the PMOS transistor is pinched off under the combined action of the substrate voltage and the gate voltage, so that the PMOS transistor has high on-resistance.
Similarly, for the NMOS transistor, the substrate voltage is connected to the ground potential, and the gate voltage is connected to the reverse enable signal, which is 0V at this time. In this case, the substrate and the gate of the NMOS transistor are both low voltage, and the NMOS transistor is also pinched off, so that the NMOS transistor has high on-resistance.
It should be noted that the first substrate control unit and the second substrate control unit in the present invention may be implemented based on MOS transistors, may also be implemented based on CMOS transmission gates, or may be any switch type commonly used in the prior art.
Preferably, the element of the first and second substrate control units, which controls the connection of the substrate of the analog switch tube in the analog switch unit and the output end of the analog switch unit, is a CMOS transmission gate; the substrates of the first and second substrate control units for controlling the analog switch tube of the analog switch unit are respectively connected with the working voltage V cc The element connected with the ground potential is a switching MOS tube.
Fig. 4 is a schematic structural diagram of a low-voltage analog switch circuit according to the present invention, in which a MOS transistor analog switch is used to implement a control switch. In one embodiment of the present invention, as shown in fig. 4, CMOS transmission gates are used to implement the switches S2 and S3 in the first and second substrate control units. For example, a CMOS transmission gate is connected between the substrate of the high-side switch tube and the output terminal of the analog switch unit, and a CMOS transmission gate is connected between the substrate of the low-side switch tube and the output terminal of the analog switch unit. To control the switches S2 and S3, the gate voltages of the MOS transistors in the CMOS transmission gate can be controlled by the inverted enable signal EN _ Bar and the enable signal EN, respectively.
It can be understood that, because the switches S2 and S3 in the substrate control unit are both implemented by the CMOS transmission gate, that is, the CMOS transmission gate includes the PMOS transistor and the NMOS transistor that are symmetrically arranged in parallel, the substrate control unit can control the substrate without the problem in the prior art shown in fig. 2, thereby stabilizing the on-resistance Ron, improving the flatness of the on-resistance, and greatly shortening the time length from the start to the stabilization of the analog switch circuit.
On the other hand, the switches S1 and S4 in the first and second substrate control units are implemented using MOS transistors. For example, a PMOS transistor is connected between the substrate of the high-side switch tube and the operating voltage Vcc, and an NMOS transistor is connected between the substrate of the low-side switch tube and the ground potential. In order to control the switches S1 and S4, the gates of the PMOS and NMOS transistors are respectively connected with a reverse enable signal EN _ Bar and an enable signal EN. Because the working voltage Vcc and the low-level potential do not cause too large influence on the value of the substrate voltage relatively, namely, the main switching tube is not switched in any working state, the MOS tube is only adopted as the switches S1 and S4 in order to save the number of circuit elements, further save the chip area and reduce the circuit complexity.
Compared with the prior art, the novel analog switch circuit has the advantages that the first substrate control unit and the second substrate control unit are added, the control over the substrate voltage of the switch tube is achieved under the condition that the switch tube is turned on and turned off respectively, the threshold voltage of the switch tube is reduced when the switch tube is turned on through the control over the substrate voltage of the MOS tube, and the switch impedance of the switch tube is increased when the switch tube is turned off.
The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.
Claims (11)
1. A low voltage analog switch circuit, characterized by:
the circuit comprises an analog switch unit, a first substrate control unit and a second substrate control unit, wherein the first substrate control unit and the second substrate control unit are respectively connected with the analog switch unit; wherein,
the first substrate control unit is used for connecting a substrate of an analog switching tube in the analog switching unit with one end of the analog switching unit so as to reduce the working voltage of the analog switching unit;
and the second substrate control unit is used for connecting the substrate of an analog switching tube in the analog switching unit with the bus voltage so as to improve the switching impedance of the analog switching unit.
2. A low voltage analog switch circuit as claimed in claim 1, wherein:
when the analog switch unit is switched on, the first substrate control unit is switched on, and the second substrate control unit is switched off;
when the analog switch unit is switched off, the first substrate control unit is switched off, and the second substrate control unit is switched on.
3. A low voltage analog switch circuit as claimed in claim 2, wherein:
the first substrate control unit controls the drain electrode of the high-end switching tube Mp1 to be connected with the substrate, so that the source substrate potential difference is larger than 0; or,
and controlling the connection of the source electrode and the substrate of the high-end switching tube Mp1 so as to eliminate the substrate bias effect of the high-end switching tube Mp 1.
4. A low voltage analog switch circuit as claimed in claim 2, wherein:
the first substrate control unit controls the connection between the source electrode of the low-side switching tube Mn1 and the substrate so as to eliminate the substrate bias effect of the low-side switching tube Mn 1; or,
and controlling the drain electrode of the low-side switching tube Mn1 to be connected with the substrate so that the potential difference between the source electrode and the substrate is less than 0.
5. A low voltage analog switch circuit as claimed in claim 3 or 4, wherein:
the first substrate control unit connects the substrate of an analog switch tube in the analog switch unit with the output end of the analog switch unit; and the number of the first and second electrodes,
when the voltage of the input end of the analog switch unit is higher than the voltage of the output end, the drain electrode of the high-end switch tube Mp1 is connected with the substrate, and the source electrode of the low-end switch tube Mn1 is connected with the substrate;
when the voltage of the input end of the analog switch unit is lower than that of the output end, the source electrode of the high-end switch tube Mp1 is connected with the substrate, and the drain electrode of the low-end switch tube Mn1 is connected with the substrate.
6. A low voltage analog switch circuit as claimed in claim 5, wherein:
when the voltage of the input end of the analog switch unit is higher than the voltage of the output end, the threshold voltage of the high-end switch tube Mp1 is
The threshold voltage of the low-end switch tube Mn1 is V thnx ＝V th0,n ；
Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set;
γ p is the body effect coefficient of the switching tube Mp1,
Φ F,p is the substrate fermi potential of the switching tube Mp1,
V in is the input terminal voltage of the analog switching unit,
V out is the output terminal voltage of the analog switch unit.
7. A low voltage analog switch circuit as claimed in claim 5, wherein:
when the voltage of the input end of the analog switch unit is lower than that of the output end, the threshold voltage of the high-end switch tube Mp1 is V thpx ＝V th0,p The threshold voltage of the low-side switching tube Mn1 is
Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 are respectively when the source-substrate voltage difference is 0;
γ n is the body effect coefficient of the switching tube Mn1,
Φ F,n is the substrate fermi potential of the switching tube Mn1,
V in is the input terminal voltage of the analog switching unit,
V out is the output terminal voltage of the analog switch unit.
8. A low voltage analog switch circuit as claimed in claim 2, wherein:
the threshold voltage of the analog switch unit is V thnx +|V thpx |<V th0,n +|V th0,p |；
Wherein, V th0,p 、V th0,n The threshold voltages of the switching tubes Mp1 and Mn1 when the source-substrate voltage difference is 0 are respectively set;
V thnx 、V thpx the threshold voltages of the switching tubes Mp1 and Mn1 under the action of the first substrate control unit are respectively.
9. A low voltage analog switch circuit as claimed in claim 8, wherein:
the analog switchThe working voltage of the unit is more than or equal to the threshold voltage V of the analog switch unit thnx +|V thpx |。
10. A low voltage analog switch circuit as claimed in claim 2, wherein:
the first substrate control unit controls the substrate of the high-end switching tube Mp1 to be connected to a working voltage V when the analog switch unit is switched off cc And controlling the substrate of the low-side switching tube Mn1 to be connected to the ground potential.
11. An analog switching circuit as claimed in claim 2, wherein:
the element which is connected with the substrate of the analog switch tube in the analog switch unit and the output end of the analog switch unit in the first and second substrate control units is a CMOS transmission gate;
the substrates of the first substrate control unit and the second substrate control unit for controlling the analog switch tubes in the analog switch unit are respectively connected with a working voltage V cc The element connected with the ground potential is a switching MOS tube.
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| CN202111203030.9A CN115987262A (en) | 2021-10-15 | 2021-10-15 | Low-voltage analog switch circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117811584A (en) * | 2024-02-29 | 2024-04-02 | 成都电科星拓科技有限公司 | Digital-to-analog converter |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117811584A (en) * | 2024-02-29 | 2024-04-02 | 成都电科星拓科技有限公司 | Digital-to-analog converter |
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