Low noise trans-impedance amplifier

This application claims priority to and incorporates by reference Chinese Patent Application No. 202210352454.X filed 4 Apr. 2022.

The present application relates to a trans-impedance amplifier (TIA), particularly to a low noise TIA.

TIAs are widely used in electronic devices such as photoelectric receivers and op-amps. Typically, a receiver front end (RXFE) of a photoelectric receiver may include a low noise amplifier (LNA), a mixer, and a TIA, for example, and noise incurred by the TIA may greatly affect the performance of the receiver. Therefore, a new TIA with reduced noise becomes highly desirable.

According to an embodiment, a TIA may comprise an input stage and an output driving stage. The input stage may comprise a first and a second input PMOS transistors; a first and a second load NMOS transistors, wherein drains of the first and the second input PMOS transistors and drains of the first and the second load NMOS transistors are electrically connected; and a first and a second differential voltage input nodes respectively electrically connected to gates of the first and the second input PMOS transistors. The output driving stage may comprise a first and a second output circuits, each of the first and the second output circuits comprising: a first pair of PMOS and NMOS transistors electrically connected in parallel; a second pair of PMOS and NMOS transistors electrically connected in series; a pair of capacitors electrically connected in series; and a differential output node electrically connected to a drain of a NMOS transistor of the second pair of PMOS and NMOS transistors.

According to an embodiment, a TIA may comprise an input stage and an output driving stage. The input stage may comprise a first and a second input PMOS transistors, a first and a second load NMOS transistors, and a first and a second differential voltage input nodes. The output driving stage may comprise a first and a second output circuits each comprising: a first pair of PMOS and NMOS transistors electrically connected in parallel; a second pair of PMOS and NMOS transistors electrically connected in series; a pair of capacitors electrically connected in series; a differential output node electrically connected to a drain of a NMOS transistor of the second pair of PMOS and NMOS transistors; and a third PMOS transistor electrically connecting a gate of the NMOS transistor of the second pair of PMOS and NMOS transistors to a drain of the first or the second input PMOS transistors of the input stage.

According to an embodiment, a receiver front end (RXFE) may comprise a low noise amplifier (LNA), a mixer, and a TIA that are electrically connected in series. The TIA may comprise an input stage and an output driving stage. The input stage may comprise a first and a second input PMOS transistors, a first and a second load NMOS transistors, and a first and a second differential voltage input nodes. The output driving stage may comprise a first and a second output circuits each comprising: a first pair of PMOS and NMOS transistors electrically connected in parallel; a second pair of PMOS and NMOS transistors electrically connected in series; a pair of capacitors electrically connected in series; a differential output node electrically connected to a drain of a NMOS transistor of the second pair of PMOS and NMOS transistors; and a third PMOS transistor electrically connecting a gate of the NMOS transistor of the second pair of PMOS and NMOS transistors to a drain of the first or the second input PMOS transistors of the input stage.

According to an embodiment, a method of amplifying a voltage signal may comprise receiving differential input voltages with a first and a second differential voltage input nodes of a trans-impedance amplifier (TIA), wherein the TIA may include an input stage comprising a first and a second input PMOS transistors; a first and a second load NMOS transistors, wherein drains of the first and the second input PMOS transistors and drains of the first and the second load NMOS transistors are electrically connected; and a first and a second differential voltage input nodes respectively electrically connected to gates of the first and the second input PMOS transistors; and an output driving stage comprising a first and a second output circuits each comprising a first pair of PMOS and NMOS transistors electrically connected in parallel; a second pair of PMOS and NMOS transistors electrically connected in series; a pair of capacitors electrically connected in series; and a differential output node electrically connected to a drain of a NMOS transistor of the second pair of PMOS and NMOS transistors. The method may also comprise amplifying the differential input voltages by the input stage and the output driving stage to create amplified differential output voltages; and outputting the amplified differential output voltages to the first and the second differential output nodes.

Non-limiting and non-exhaustive embodiments of the present application are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

FIG. 1 is a drawing illustrating a RXFE including a TIA according to an embodiment.

FIG. 2 is a circuit diagram illustrating a TIA according to an embodiment.

FIG. 3 is a circuit diagram illustrating a TIA according to another embodiment.

FIG. 4 is a flowchart illustrating a method of low noise amplification.

Various aspects and examples of the application will now be described. The following description provides specific details for a thorough understanding and enabling description of these examples. Those skilled in the art will understand, however, that the application may be practiced without many of these details.

Additionally, some well-known structures or functions may not be shown or described in detail, to avoid unnecessarily obscuring the relevant description.

The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific examples of the application. Certain terms may even be emphasized below, however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section. Hereinafter, “PM” or “MP” may represent PMOS transistors, and “NM” or “MN” may represent NMOS transistors.

Without loss of generality, reference will be made to illustrative embodiments by taking a TIA and a RXFE including the TIA as example. Those of ordinary skills in the art understand that this is only to describe the application clearly and adequately, rather than limit the scope of the application, which is defined by the appended claims.

FIG. 1 is a drawing illustrating a RXFE 100 of a receiver according to an embodiment of the application. As shown in FIG. 1 , the RXFE 100 of the receiver (e.g., a photoelectric receiver not shown) includes an LNA 1 , a mixer 2 (e.g., a passive mixer), and a TIA 3 , which are all connected in series. The RXFE 100 also includes a feedback resistor Rf that is electrically connected to the TIA 3 in parallel. In some embodiments, an antenna 4 is electrically connected to the LNA 1 of the RXFE 100 . Rs represents a parasitic equivalent resistor on a connection line.

The LNA 1 normally works at a high frequency (HF), while the TIA 3 normally works at a medium frequency (MF) or a low frequency (LF). For example, the LNA 1 works at a higher frequency than the TIA 3 . For example, the LNA 1 receives a HF voltage signal V nLNA and outputs to the mixer 2 a HF current signal, which is thus transformed by the mixer 2 into a MF or LF current signal I LNA that is output to the TIA 3 . After that, the TIA 3 transforms the current signal I LNA into a MF or LF voltage signal V out (e.g., V out =I LNA *R f ) and outputs the voltage signal V out to a following circuit (a filter, for example) to make further operations.

The total noise level of RXFE 100 of the receiver is mainly determined by both the LNA 1 and the TIA 3 , e.g., in a situation that the mixer 2 is passive. Thus, the total noise level of RXFE 100 can be greatly suppressed by reducing the noise incurred by the TIA 3 .

Referring to Equation (1) as shown below, F total represents a total noise factor of the RXFE 100 , V nLNA represents an input voltage of the LNA 1 , V nTIA represents an input voltage of the TIA 3 , AV LNA represents an open loop gain of the LNA 1 , and Rs represents the parasitic equivalent resistor on the connection line. Rs may cause a heat noise, which may greatly affect the noise level of the RXFE 100 and can be simulated by an equivalent noise voltage V nRs . For example, V nRs =4kTR s , here k is a Boltzmann constant, and T is a Kelvins temperature.

FIG. 2 is a circuit diagram illustrating a TIA 200 according to an embodiment of the application. For example, the TIA 200 may include a first stage (e.g., an input stage, “IS”) and a second stage (e.g., an output driving stage, “ODS”).

As shown in FIG. 2 , the first stage (IS) of the TIA 200 includes a pair of differential input PMOS transistors PM 1 and PM 2 , a pair of load NMOS transistors NM 1 and NM 2 , and a pair of differential voltage input nodes V inp and V inn that are respectively electrically connected to gates of the pair of PM 1 and PM 2 to respectively receive differential input voltages from outside (e.g., from another circuit).

In some embodiments, sources of the pair of PM 1 and PM 2 of the first stage are electrically connected to a common point A, and can receive a DC bias current I d1 that may ensure the first stage to work at a suitable current working condition. In some embodiments, sources of the pair of NM 1 and NM 2 of the first stage are electrically connected to a common point E, which can be grounded.

In some embodiments, drains of PM 1 and NM 1 are electrically connected to a point B 1 , while drains of PM 2 and NM 2 are electrically connected to a point B 2 , and thus the pair of PM 1 and PM 2 and the pair of NM 1 and NM 2 in the first stage can determine the total gain of the first stage of the TIA 200 .

As shown in FIG. 2 , the first stage (IS) includes a first branch including PM 1 and NM 1 electrically connected in series, and a second branch including PM 2 and NM 2 electrically connected in series. The first branch and the second branch are electrically connected in parallel.

As shown in FIG. 2 , the second stage (ODS) of the TIA 200 includes a pair of a first output circuit OC 1 and a second output circuit OC 2 respectively including a pair of differential output nodes V outp and V outc to output the amplified differential voltages to another circuit. In some embodiments, both of the OC 1 and the OC 2 of the second stage may receive a DC bias current I clamp that may ensure the second stage to work at a suitable current working condition.

In some embodiments, the OC 1 may include a pair of MP 3 and MN 3 , a pair of capacitors C 1 and C 3 , and a pair of MP 5 and NMp, which are electrically connected in parallel.

In the pair of MP 3 and MN 3 , MP 3 and MN 3 are electrically connected in parallel. The drain of MN 3 and the source of MP 3 are electrically connected to a common point D 1 , and can receive the DC bias I clamp . The source of MN 3 and the drain of MP 3 are electrically connected to the common point B 1 .

In the pair of capacitors C 1 and C 3 , C 1 and C 3 are electrically connected in series between the common points D 1 and B 1 .

In the pair of MP 5 and NMp, the gate of MP 5 is electrically connected to the common point D 1 , drains of MP 5 and NMp are electrically connected to a common point G 1 , and the gate of NMp is electrically connected to the common point B 1 .

The OC 1 also may include a resistor R 1 electrically connected between the common point G 1 and a common point F 1 , the F 1 being electrically connected between the capacitors C 1 and C 3 . R 1 , C 1 and C 3 can provide a miller compensation to the positive output node V outp of the OC 1 .

The OC 2 may have a structure similar to that of OC 1 . In some embodiments, the OC 2 may include a pair of MP 4 and MN 4 , a pair of capacitors C 2 and C 4 , and a pair of MP 6 and NMn, which are electrically connected in parallel.

In the pair of MP 4 and MN 4 , MP 4 and MN 4 are electrically connected in parallel. The drain of MN 4 and the source of MP 4 are electrically connected to a common point D 2 , and can receive the DC bias I clamp . The source of MN 4 and the drain of MP 4 are electrically connected to the common point B 2 .

In the pair of capacitors C 2 and C 4 , C 2 and C 4 are electrically connected in series between the common points D 2 and B 2 .

In the pair of MP 6 and NMn, the gate of MP 6 is electrically connected to the common point D 2 , drains of MP 6 and NMn are electrically connected to a common point G 2 , and the gate of NMn is electrically connected to the common point B 2 .

The OC 2 also may include a resistor R 2 electrically connected between the common point G 2 and a common point F 2 , the F 2 being electrically connected between C 2 and C 4 . R 2 , C 2 and C 4 can provide a miller compensation to the negative output node V outn of the OC 1 .

The OC 1 and OC 2 of the second stage may further amplify the signals (e.g., differential voltage signals) that have been amplified by the first stage, and output the further amplified signals to the differential output nodes V outp and V outn .

In FIG. 2 , I d1 represents a DC bias current supplied to the first stage, and I n1 and I n2 respectively represent thermal noise currents passing through the PM 1 and the PM 2 :

I n1 2 =4 kTγg mp1

I n2 2 =4 kTγg mp2

Referring to Equation (2), DC bias currents passing through the PM 1 and the PM 2 are the same, i.e., g mp1 =g mp2 =g mp , thus I n1 2 =I n2 2 =4kTγg mp . Accordingly, the noise voltage equivalent to the input end is:

FIG. 3 is a circuit diagram illustrating a TIA 300 according to another embodiment. The TIA 300 includes a first stage (e.g., an input stage, “IS”) and a second stage (e.g., an output driving stage, “ODS”). The first stage of the TIA 300 includes a pair of differential input PMOS transistors PM 1 and PM 2 , a pair of differential input NMOS transistors NM 1 and NM 2 , and a pair of differential voltage input nodes V inp and V inn to receive differential input voltages (e.g., from another circuit).

In some embodiments, the V inp node is electrically connected to gates of both the PM 1 and NM 1 , and thus can supply an input voltage V inp to the gates of both the PM 1 and NM 1 . The V inn node is electrically connected to gates of both the PM 2 and NM 2 , and thus can supply an input voltage V inn to the gates of both the PM 2 and NM 2 .

In some embodiments, sources of the pair of PM 1 and PM 2 of the first stage (IS) are electrically connected to a common point A, and may receive a DC bias current I d1 to ensure the first stage to work at a suitable current working condition. In some embodiments, sources of the pair of NM 1 and NM 2 of the first stage are electrically connected to a common point E, which can be grounded.

In some embodiments, drains of PM 1 and NM 1 are electrically connected to a point B 1 , and drains of the PM 2 and the NM 2 are electrically connected to a common point B 2 . Thus, the pair of PM 1 and PM 2 as well as the pair of NM 1 and NM 2 of the first stage can determine the total gain of the first stage of the TIA 300 .

As shown in FIG. 3 , the second stage (ODS) of the TIA 300 includes a pair of a first output circuit OC 1 and a second output circuit OC 2 respectively including differential output nodes V outp and V outn to output the amplified differential voltages to another circuit. Both of the OC 1 and the OC 2 of the second stage may receive a DC bias current I clamp that may ensure the second stage to work at a suitable current working condition.

The OC 1 may include a pair of MP 3 and MN 3 . The drain of MN 3 and the source of MP 3 are electrically connected to a common point D 1 , and can receive the DC bias I clamp . The source of MN 3 and the drain of MP 3 are electrically connected to a common point H 1 .

The OC 1 also may include a pair of capacitors C 1 and C 3 that are electrically connected in series between the common points D 1 and H 1 .

The OC 1 also may include a pair of MP 5 and MNp. The gate of PM 5 is electrically connected to the common point D 1 , drains of MP 5 and MNp are electrically connected to a common point G 1 , and the gate of MNp is electrically connected to the common point H 1 .

The OC 1 also may include a resistor R 1 and a capacitor C 5 electrically connected in series between the common points G 1 and B 1 , the B 1 being electrically connected between the capacitors C 1 and C 3 . R 1 , C 1 , C 3 and C 5 can provide a miller compensation to the positive output node V outp of the OC 1 .

The OC 1 also may include a MP 7 electrically connected between the common points H 1 and B 1 . The source of MP 7 is electrically connected to the common point B 1 , and the drain of MP 7 is electrically connected to the common point H 1 .

The OC 1 and OC 2 have similar structures. In some embodiments, the OC 2 may include a pair of MP 4 and MN 4 . The drain of MN 4 and the source of MP 4 are electrically connected to a common point D 2 , and can receive the DC bias I clamp . The source of MN 4 and the drain of MP 4 are electrically connected to a common point H 2 .

The OC 2 also may include a pair of capacitors C 2 and C 4 that are electrically connected in series between the common points D 2 and H 2 .

The OC 2 also may include a pair of MP 6 and MNn. The gate of MP 6 is electrically connected to the common point D 2 , drains of MP 6 and MNn are electrically connected to a common point G 2 , and the gate of MNn is electrically connected to the common point H 2 .

The OC 2 also may include a resistor R 2 and a capacitor C 6 electrically connected in series between the common points G 2 and B 2 , the B 2 being electrically connected between the capacitors C 2 and C 4 . R 2 , C 2 , C 4 and C 6 can provide a miller compensation to the negative output node V outn of the OC 1 .

The OC 2 also may include a MP 8 electrically connected between the common points H 2 and B 2 . The source of MP 8 is electrically connected to the common point B 2 , and the drain of MP 8 is electrically connected to the common point H 1 .

As shown in FIG. 3 , both of the pair of OC 1 and OC 2 of the second stage may receive a DC bias current I clamp to ensure the second stage to work at a suitable current working condition. The OC 1 and the OC 2 of the second stage may further amplify the signals (e.g., differential voltage signals) that already have been amplified by the first stage, and may output the further amplified signals to the pair of differential output nodes V outp and V outn in order to output to a following circuit (such as a filter).

In FIG. 3 , I d1 represents a bias current supplied to the first stage, and I n1 , I n2 , I n3 , and I n4 respectively represent thermal noise currents passing through the input transistors PM 1 , PM 2 , NM 3 , and NM 4 :

I n1 2 =4 kTγg mp1

I n2 2 =4 kTγg mp2

I n3 2 =4 kTγg mn3

I n4 2 =4 kTγg mn4

Referring to Equation (3), DC bias currents on the input transistors PM 1 , PM 2 , NM 3 , and NM 4 are the same, i.e., g mp1 =g mp2 =g mp , g mn3 =g mn4 =g mn , I n1 2 =I n2 2 =4kTγg mp , I n3 2 =I n4 2 =4kTγg mn , thus, the noise voltage equivalent to the input end is:

Comparing Equation (2) and Equation (3), the structure of the TIA 300 with the additional pair of input NMOS transistors NM 3 and NM 4 can reduce the equivalent input thermal noise voltage under the same DC bias current. Therefore, the TIA 300 may incur a reduced noise voltage to the RXFE, and thus may reduce the total noise level of the RXFE.

FIG. 4 is a flowchart illustrating a method 400 of low noise amplification by using a TIA (e.g., TIA 200 as shown in FIG. 2 , or TIA 300 as shown in FIG. 3 ) including a first stage (e.g., an input stage) and a second stage (e.g., an output driving stage). In an embodiment, in block 402 , receiving differential input voltages (e.g., from outside) as an input signal by a pair of differential voltage input nodes V inp and V inn in the first stage of the TIA, in block 404 , amplifying the differential input voltages by both the first stage and the second stage of the TIA to create amplified differential output voltages, and in block 406 , outputting the amplified differential output voltages to a pair of differential output nodes V outp and V outn in the second stage of the TIA to obtain an amplified signal with reduced noise level as discussed above.

Features and aspects of various embodiments may be integrated into other embodiments, and embodiments illustrated in this document may be implemented without all of the features or aspects illustrated or described.

One skilled in the art will appreciate that although specific examples and embodiments of the system and methods have been described for purposes of illustration, various modifications can be made without deviating from the spirit and scope of the present application. Moreover, features of one embodiment may be incorporated into other embodiments, even where those features are not described together in a single embodiment within the present document. Accordingly, the application is described by the appended claims.