Patent ID: 12191831

DETAILED DESCRIPTION

The following detailed description references the accompanying figures in describing embodiments consistent with this disclosure. The examples of the embodiments are provided for illustrative purposes and are not exhaustive. Additional embodiments not explicitly illustrated or described are possible. Further, modifications can be made to presented embodiments within the scope of the present teachings. The detailed description is not meant to limit this disclosure. Rather, the scope of the present disclosure is defined only in accordance with the presented claims and equivalents thereof.

FIG.2is a circuit diagram illustrating an amplifying device1000according to an embodiment of the present disclosure.

The amplifying device1000includes a main amplifier10, a first feedback circuit20, an input coupling circuit30, and a bias circuit40.

The main amplifier10is a differential amplifier and includes differential input terminals and differential output terminals.

The first feedback circuit20forms a negative feedback loop between the input and output terminals of the main amplifier10and includes first feedback capacitors21. The input coupling circuit30includes input capacitors30coupled between first nodes N11and N12and the input terminals of the main amplifier10. The bias circuit40applies a common voltage VCOMto the input terminals of the main amplifier10through resistors40.

The amplifying device1000may additionally perform a chopping operation according to a chopping frequency fCHOPto suppress noise and offset.

To this end, the main amplifier10includes a first chopping circuit11therein, and the first feedback circuit20may further include a second chopping circuit22. A third chopping circuit31coupled between input terminals of the entire circuit and the input coupling circuit30may be further included.

The amplifying device1000may further include a second feedback circuit50to increase input impedance.

The second feedback circuit50forms a positive feedback loop between the input and output terminals of the main amplifier10, includes a second feedback capacitor51, and may further include a fourth chopping circuit52for chopping operation.

The amplifying device1000further includes an amplifying feedback circuit100.

The feedback amplifier110includes a feedback amplifier110, a feedback output capacitors120, and a feedback input capacitors130.

The feedback amplifier110is a differential amplifier and includes differential input terminals and differential output terminals.

The amplifying feedback circuit100increases input impedance of the amplifying device1000.

The amplifying feedback circuit100feeds output signals of the main amplifier10back to the first nodes N11and N12.

The first nodes N11and N12include an eleventh node N11coupled to a positive input terminal of the main amplifier10and a twelfth node N12coupled to a negative input terminal of the main amplifier10.

In the present embodiment, when chopping operation is not performed, a positive output signal among the differential output signals of the feedback amplifier110is coupled to the twelfth node N12, and a negative output signal among the differential output signals of the feedback amplifier110is coupled to the eleventh node N11.

Accordingly, the amplifying feedback circuit100performs a negative feedback operation.

The feedback output capacitors120couples the output terminals of the feedback amplifier110and the first nodes N11and N12.

The feedback input capacitors130couples the input terminals of the feedback amplifier110and the output terminals of the main amplifier10.

In this embodiment, an input terminals and an output terminals of the feedback amplifier110are coupled via the amplifying feedback capacitors141and142.

The amplifying feedback capacitor141couples the positive output terminal and the negative input terminal of the feedback amplifier110, and the amplifying feedback capacitor142couples the negative output terminal and the positive input terminal of the feedback amplifier110.

The amplifying feedback circuit100may further include a fifth chopping circuit150for a chopping operation.

The fifth chopping circuit150may be coupled between the output terminals of the main amplifier10and the feedback input capacitors130and operates according to the chopping frequency fCHOP.

As described above, leakage current cannot be compensated because of parasitic capacitors present in the first nodes N11and N12.

In the present embodiment, the amplifying feedback circuit100further increases input impedance by compensating for the leakage current by the parasitic capacitors present in the first nodes N11and N12.

The input impedance of the amplifying device1000may be expressed as in Equation 3.

Zi⁢⁢n=1s[Cp-(Gm⁢⁢axN-Gm⁢⁢axG-1)⁢Cunit][Equation⁢⁢3]

Equation 3 assumes the following conditions.

Gmaxis the maximum closed loop gain of the main amplifier10with first feedback loop20, which is assumed to be 128 in this embodiment, and the gain of the amplifying device1000is indicated by G.

Each of the capacitance C1of the feedback input capacitor130, the capacitance Cfbof the first feedback capacitor21, and the capacitance Cpfof the second feedback capacitor51corresponds to the capacitance Cinof the input capacitor included in the input coupling circuit30divided by the gain G of the amplifying device1000.

The capacitance Cinof the input capacitor included in the input coupling circuit30corresponds to Gmaxtimes the unit capacitance Cunit.

The capacitance C2of the feedback output capacitor120is equal to the unit capacitance Cunit, and the capacitance C3of the amplifying feedback capacitors141and142is N times the unit capacitance Cunit, where N is a natural number.

Equations 1 and 3 can be used to compare effects of the conventional amplifying device1and the amplifying device1000according to the present embodiment.

Conventionally, input impedance is limited due to the parasitic capacitance Cp.

In the present embodiment, since there is a term that cancels the parasitic capacitance Cpregardless of the voltage gain, it is possible to sufficiently increase the input impedance by reducing the influence of the parasitic capacitance Cp.

In addition, by appropriately selecting the unit capacitance Cunitand N, the input impedance can be sufficiently increased even when the gain G of the amplifying device2000is small.

FIG.3shows an amplifying device2000according to an embodiment of the present disclosure.

The amplifying device2000ofFIG.3is substantially the same as the amplifying device1000ofFIG.2except that it further includes a chopping circuits161and162.

In the embodiment ofFIG.3, the amplifying feedback circuit100-1further includes a sixth chopping circuit161between the output terminals of the feedback amplifier110and the feedback output capacitors120, and a seventh chopping circuit162between the feedback input capacitors130and the input terminals of the feedback amplifier110.

In the embodiment ofFIG.3, noise and offset of the feedback amplifier110may be further suppressed by the additional chopping operation of the sixth chopping circuit161and the seventh chopping circuit162.

Since the input impedance boosting effect of the amplifying device2000is substantially the same as that of the amplifying device1000, a repetitive description will be omitted.

FIG.4shows an amplifying device3000andFIG.5shows an amplifying device4000according to embodiments of the present disclosure.

The amplifying device3000ofFIG.4is a circuit in which the second feedback circuit50is omitted from the amplifying device1000ofFIG.2, and the amplifying device4000ofFIG.5is a circuit in which the second feedback circuit50is omitted from the amplifying device2000ofFIG.3.

Since the detailed circuit configuration is the same as described above, repeated description thereof will be omitted.

When the second feedback circuit50is omitted, the input impedance is changed like Equation 4.

Zi⁢⁢n=1s[Cp+N-1N⁢Ci⁢⁢n+Cunit][Equation⁢⁢4]

By setting the value of N to 1 in Equation 4, the influence of the input capacitance Cincan be canceled.

This can relieve the limitation of input impedance due to input capacitance.

FIGS.6and7are graphs showing effects of the present embodiment.

InFIGS.6and7, the horizontal axis indicates frequency and the vertical axis indicates impedance.

FIG.6corresponds to a case in which the closed loop gain of the amplifying device is 128, andFIG.7corresponds to a case in which the closed loop gain of the amplifying device is 8.

InFIGS.6and7, the dotted line represents input impedance of the conventional amplifying device, and the solid line represents input impedance of the amplifying device according to a present embodiment. It can be seen that the impedance boosting effect of an amplifying device according to the present embodiment is large compared to conventional amplifying device.

In addition, it can be seen fromFIGS.6and7that, in the case of the present embodiment, the impedance boosting effect is larger than that of the conventional amplifying device even when the gain of the amplifying device is small.

Although various embodiments have been described for illustrative purposes, it will be apparent to those skilled in the art that various changes and modifications may be made to the described embodiments without departing from the spirit and scope of the disclosure as defined by the following claims.