A current-mode transmitter front-end circuit and a transmission system

Abstract

The present invention discloses a current-mode transmitter front-end circuit and a transmission system. The front-end circuit includes: a baseband signal converter, a current-mode mixer, a power amplifier, and a balun module; the baseband signal converter is connected to the power amplifier through the current-mode mixer, and the power amplifier is connected to the balun module; the baseband signal converter is configured to convert a plurality of input baseband voltage signals into a plurality of reference current signals for output; the current-mode mixer mixes the plurality of reference current signals with a local oscillator signal to generate a radio frequency current signal; the power amplifier is used to amplify and output the radio frequency current signal; the balun module is used to convert the radio frequency current signal output by the power amplifier into an output voltage, and at the same time convert the differential output into a single-ended output. The present invention improves the linearity of the mixer at higher input powers, suppresses the local oscillator leakage, improves the quality of the transmitted signal, and enables a higher saturated output power.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency integrated circuits, and particularly to a current-mode transmitter front-end circuit and a transmission system. Background Art

[0002] With the increasing requirements of wireless communication systems for data throughput, communication systems must use more advanced modulation techniques, such as 64QAM, 256QAM, etc.; these advanced modulation techniques can transmit more bits per unit time, but also have higher requirements for signal quality and channel conditions, and the most important point is that the communication system is required to have high linearity.

[0003] In a traditional transmission system, a mixer up-converts a baseband signal to a radio frequency signal by mixing the baseband signal with a high-frequency clock, and the radio frequency signal is amplified by an on-chip power amplifier and output to a receiving system to complete the communication function. All transmissions on this path are voltage-mode transmissions, so a large voltage swing will be generated on the mixer implemented by NMOS transistors (usually a Gilbert cell); according to the device principle of NMOS transistors, the NMOS transistors constituting the mixer will have large signal distortion under large signals; and in a differential system, the change in semiconductor manufacturing process causes size mismatch between two corresponding transconductance elements, resulting in DC offset, which in turn causes local oscillator leakage, which will deteriorate the reception quality of the receiving system.

[0004] Therefore, the traditional transmission system cannot meet the requirements of the communication system for linearity when using advanced modulation techniques. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a current-mode transmitter front-end circuit and a transmission system, which can meet the requirements of the communication system for linearity when using advanced modulation techniques.

[0006] To solve the above problems, the present invention is implemented according to the following solutions:

[0007] A current-mode transmitter front-end circuit is provided, including: a baseband signal converter, a current-mode mixer, a power amplifier, and a balun module; the baseband signal converter is connected to the power amplifier through the current-mode mixer, and the power amplifier is connected to the balun module;

[0008] The baseband signal converter is configured to convert a plurality of input baseband voltage signals into a plurality of reference current signals for output; the current-mode mixer mixes the plurality of reference current signals with a local oscillator signal to generate a radio frequency current signal; the power amplifier is configured to amplify and output the radio frequency current signal; the balun module is configured to convert the radio frequency current signal output by the power amplifier into an output voltage, and at the same time convert the differential output into a single-ended output.

[0009] Compared with the prior art, the beneficial effects of a current-mode transmitter front-end circuit of the present invention are as follows: The baseband voltage signal is converted into a reference current signal through a baseband signal converter, and the traditional voltage-mode mixer is changed into a current-mode mixer, so that the mixer does not transmit voltage, and large voltage swings will not be generated, improving the linearity of the mixer at higher input powers. The transmitter front-end circuit performs current amplification throughout the process of mixing and amplification, and only converts it into a return voltage for output at the output, avoiding the nonlinear components brought by the transmission of large-signal voltages, improving the quality of the transmitted signal and enabling a higher saturated output power.

[0010] Optionally, the baseband signal converter includes a plurality of conversion units; the conversion unit includes a baseband signal input branch, an operational amplifier, and a reference current output branch;

[0011] The input end of the baseband signal input branch is connected to the baseband voltage signal; the input end of the operational amplifier is connected to the output end of the baseband signal input branch, the input end of the reference current output branch, and the supply voltage; the output end of the operational amplifier is connected to the output end of the reference current output branch and the input end of the current-mode mixer.

[0012] Optionally, the input end of the operational amplifier is connected to a common-mode voltage, and the common-mode voltage is used to clamp the input signal of the operational amplifier at the same level as the common-mode voltage.

[0013] Optionally, the baseband signal input branch includes a first resistor;

[0014] The first end of the first resistor is connected to the baseband voltage signal; the second end of the first resistor is connected to the input end of the operational amplifier.

[0015] Optionally, the reference current output branch includes a first NMOS transistor;

[0016] The drain of the first NMOS transistor is connected to the input end of the operational amplifier; the gate of the first NMOS transistor is connected to the output end of the operational amplifier; the source of the first NMOS transistor is grounded.

[0017] Optionally, the current-mode mixer includes a plurality of mirror current generation branches and a plurality of mixing units;

[0018] The input end of the mirror current generating branch is connected to the output end of the operational amplifier; the output end of the mirror current generating branch is connected to the input end of the mixing unit; the input end of the mixing unit is connected to the local oscillator, and the local oscillator is used to provide the local oscillator signal; the output end of the mixing unit is connected to the input end of the power amplifier.

[0019] Optionally, the mirror current generating branch includes a second NMOS transistor;

[0020] The gate of the second NMOS transistor is connected to the output end of the operational amplifier; the drain of the second NMOS transistor is connected to the input end of the mixing unit; the source of the second NMOS transistor is grounded.

[0021] Optionally, the mixing unit includes a third NMOS transistor and a fourth NMOS transistor;

[0022] The source of the third NMOS transistor and the source of the fourth NMOS transistor are respectively connected to the drain of the second NMOS transistor; the drain of the third NMOS transistor and the drain of the fourth NMOS transistor are respectively connected to the input end of the power amplifier; the gate of the third NMOS transistor and the gate of the fourth NMOS transistor are respectively connected to the local oscillator.

[0023] Optionally, the power amplifier includes a fifth NMOS transistor and a sixth NMOS transistor;

[0024] The source of the fifth NMOS transistor is connected to the drain of the third NMOS transistor; the source of the sixth NMOS transistor is connected to the drain of the fourth NMOS transistor; the gates of the fifth NMOS transistor and the sixth NMOS transistor are respectively connected to the balun module; the gates of the fifth NMOS transistor and the sixth NMOS transistor are respectively connected to the bias voltage.

[0025] A transmitting system is further provided, including the current-mode transmitter front-end circuit described above. Description of the Drawings

[0026] Figure 1 It is a block diagram of the front-end circuit of the present invention;

[0027] Figure 2 It is the circuit of the front-end circuit of the present invention Figure 1 ;

[0028] Figure 3 It is the circuit of the front-end circuit of the present invention Figure 2 ;

[0029] Figure 4 It is the circuit of the front-end circuit of the present invention Figure 3 .

[0030] Explanation of the reference numerals: 1. baseband signal converter; 101. conversion unit; 1011. baseband signal input branch; 1012. operational amplifier; 1013. reference current output branch; 2. current-type mixer; 201. mirror current generating branch; 202. mixing unit; 3. power amplifier; 4. balun module. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0033] See also Figure 1 As shown, the present invention provides a current-type transmitter front-end circuit, including: a baseband signal converter 1, a current-type mixer 2, a power amplifier 3, and a balun module 4; the baseband signal converter 1 is connected to the power amplifier 3 through the current-type mixer 2, and the power amplifier 3 is connected to the balun module 4.

[0034] The baseband signal converter 1 is used to convert the input baseband voltage signals V BB Converted into several reference current signals I S Output, the input of baseband signal converter 1 and the common mode voltage V CM Connection, common mode voltage V CM Used to convert the baseband voltage signal V BB clamped at the common-mode voltage V CM The same level; the current type mixer 2 is based on several reference current signals I S , mixed with the local oscillator signal LO to generate the RF current signal I out1 ; Power amplifier 3 and bias voltage V BN connected so that the power amplifier 3 operates in a common gate amplification state, thereby enabling the power amplifier 3 to convert the RF current signal I out1 The output is amplified and the current signal after output is I out2; The balun module 4 is used to convert the radio frequency current signal output by the power amplifier 3, and at the same time convert the differential output to a single-ended output, that is, convert the current signal I out2 into a single-ended output voltage V out ; The input end of the baseband signal converter 1 and the input end of the balun module 4 are both connected to the supply voltage V DD The supply voltage V DD is used to provide the power supply voltage for the baseband signal converter 1 and the balun module 4.

[0035] See Figure 2 As shown, the signal processing circuits for the I-channel and Q-channel are shown, where V BB_IP is the positive signal of the I-channel baseband voltage signal, V BB_IN is the negative signal of the I-channel baseband voltage signal, V BB_QP is the positive signal of the Q-channel baseband voltage signal, V BB_QN is the negative signal of the Q-channel baseband voltage signal, that is Figure 2 the V BB_IP , V BB_IN , V BB_QP , V BB_QN all correspond to Figure 1 the baseband voltage signal V BB in; I S_IP is the positive signal of the I-channel reference current signal, I S_IN is the negative signal of the I-channel reference current signal, I S_QP is the positive signal of the Q-channel reference current signal, I S_QN is the negative signal of the Q-channel reference current signal, that is Figure 2 the I S_IP , I S_IN , I S_QP , I S_QN all correspond to Figure 1 the reference current signal I S in; LO+ is the positive signal of the local oscillator signal, LO- is the negative signal of the local oscillator signal, that is Figure 2 the LO+ and LO- in all correspond to Figure 1 the local oscillator signal LO in; I out1_P is the positive signal of the radio frequency current signal, I out1_N is the negative signal of the radio frequency current signal, that is Figure 2 the I out1_P , I out1_N all correspond to Figure 1 the radio frequency current signal in; I out2_P is the positive signal of the radio frequency current signal amplified by the power amplifier 3, I out2_N is the negative signal of the radio frequency current signal amplified by the power amplifier 3, that is Figure 2 the I out2_P , Iout2_N correspond to Figure 1 the current signal I in out2 .

[0036] In the signal processing circuits of both the I path and the Q path, there is a conversion unit 101 respectively. The conversion unit 101 is used to convert the positive signal V of the baseband voltage signal of the I path BB_IP and the negative signal V BB_IN , respectively, into the positive signal I of the reference current signal of the I path S_IP and the negative signal I S_IN and output them; convert the positive signal V of the baseband voltage signal of the Q path BB_QP and the negative signal V BB_QN , respectively, into the positive signal I of the reference current signal of the Q path S_QP and the negative signal I S_QN and output them.

[0037] In the signal processing circuits of both the I path and the Q path, there is a current mixer 2 respectively. Among them, Mix_I is the current mixer 2 of the I path, Mix_Q is the current mixer 2 of the Q path, and the output end of the current mixer 2 Mix_I of the I path is connected to the output end of the current mixer 2 Mix_Q of the Q path, that is, the current mixers 2 of the I path and the Q path have the same output end, and both output the positive signal I of the radio frequency current signal out1_P and the negative signal I out1_N ; the current mixer 2 is used to mix the positive signal I of the reference current signal of the I path S_IP , or the positive signal I of the reference current signal of the Q path S_QP , respectively, with the local oscillator signal LO+ to generate the positive signal I of the radio frequency current signal out1_P and output it; mix the negative signal I of the reference current signal of the I path S_IN , or the negative signal I of the reference current signal of the Q path S_QN , respectively, with the local oscillator signal LO- to generate the negative signal I of the radio frequency current signal out1_N and output it.

[0038] On the basis that the current mixers 2 of the I path and the Q path have the same output end and both output the positive signal I of the radio frequency current signal out1_P and the negative signal I out1_N , the current transmitter front-end circuit of the present invention only includes a power amplifier 3. The power amplifier 3 is used to respectively perform power amplification on the positive signal I of the radio frequency current signal out1_P and the negative signal I out1_N , and then output the positive signal I of the current signal out2_P and the negative signal I out2_N .

[0039] In the current-mode transmitter front-end circuit provided by the present invention, several conversion units 101 included in the baseband signal converter 1, the current-mode mixer 2, and the power amplifier 3 all have a differential-input and differential-output structure. Then, through the balun module 4, the positive signal I of the current signal output by the power amplifier 3 out2_P and the negative signal I out2_N are converted into an output voltage V with single-ended output out .

[0040] See Figure 3 shown in the figure, which is the signal processing circuit when the baseband voltage signal V BB of the I channel. The conversion unit 101 includes a baseband signal input branch 1011, an operational amplifier 1012, and a reference current output branch 1013; the current-mode mixer 2 includes several mirror current generation branches 201, that is, several mixing units 202.

[0041] The input end of the baseband signal input branch 1011 is connected to the baseband voltage signal V BB ; the input end of the operational amplifier 1012 is connected to the output end of the baseband signal input branch 1011, the input end of the reference current output branch 1013, and the supply voltage; the output end of the operational amplifier 1012 is connected to the output end of the reference current output branch 1013 and the input end of the current-mode mixer 2; the input end of the operational amplifier 1012 is connected to the common-mode voltage V CM , and the common-mode voltage V CM is used to clamp the input signal of the operational amplifier 1012 at the same level as the common-mode voltage V CM , that is, to clamp the positive signal V BB_IP and the negative signal V BB_IN of the baseband voltage signal at the same level as the common-mode voltage V CM , that is, the voltage at point A (V BB_IN ) and the voltage at point B (V BB_IP ) are at the same level as the common-mode voltage V CM , and its expression is as follows:

[0042] V BB_IN =V A =V CM =V B =V BB_IP

[0043] Among them, V A is the voltage at point A, and V B is the voltage at point B.

[0044] The operational amplifier 1012 is used to convert the baseband voltage signal V BB into a reference current signal I S, that is, the operational amplifier 1012 converts the positive signal V of the baseband voltage signal input to the positive input terminal into the positive signal I of the reference current signal BB_IP and outputs it at the positive output terminal, and converts the negative signal V of the baseband voltage signal input to the negative input terminal into the negative signal I of the reference current signal S_IP and outputs it at the negative output terminal. BB_IN S_IN S_IN

[0045] The input terminal of the mirror current generation branch 201 is connected to the output terminal of the operational amplifier 1012, that is, the input terminal of the mirror current generation branch 201 is connected to the reference current signal I S ; the output terminal of the mirror current generation branch 201 is connected to the input terminal of the mixing unit 202, that is, the input terminal of the mixing unit 202 is connected to the reference current signal I S ; the input terminal of the mixing unit 202 is connected to the local oscillator, and the local oscillator is used to provide the local oscillator signal, that is, the input terminal of the mixing unit 202 is connected to the local oscillator signal LO; the output terminal of the mixing unit 202 is connected to the input terminal of the power amplifier 3, that is, the input terminal of the power amplifier 3 is connected to the radio frequency current signal I out1 out1

[0046]

[0046] In Figure 3 the signal processing circuit shown when the baseband voltage signal V BB is the I-channel, it includes the positive signal processing circuit and the negative signal processing circuit of the I-channel. The positive signal processing circuit and the negative signal processing circuit respectively include a baseband signal input branch 1011, a reference current output branch 1013, and a current-mode mixer 2. The positive signal processing circuit and the negative signal processing circuit share an operational amplifier 1012, a power amplifier 3, and a balun module 4.

[0047] In the negative signal processing circuit when the baseband voltage signal V BB is the I-channel:

[0048] The baseband signal input branch 1011 includes a first resistor R11; the reference current output branch 1013 includes a first NMOS transistor NM11; the mirror current generation branch 201 includes a second NMOS transistor NM21; the mixing unit 202 includes a third NMOS transistor NM25 and a fourth NMOS transistor NM26; the power amplifier 3 includes a fifth NMOS transistor NM31 and a sixth NMOS transistor NM32.

[0049] The first end of the first resistor R11 is connected to the negative signal V of the baseband voltage signal BB_IN ; the second end of the first resistor R11 is connected to the negative input terminal of the operational amplifier 1012, that is, the negative input terminal of the operational amplifier 1012 is connected to the negative signal V of the baseband voltage signal BB_INConnection; the drain of the first NMOS transistor NM11 is connected to the negative input terminal of the operational amplifier 1012; the gate of the first NMOS transistor NM11 is connected to the negative output terminal of the operational amplifier 1012, that is, the gate of the first NMOS transistor NM11 is connected to the negative signal I of the reference current signal S_IN Connection; the source of the first NMOS transistor NM11 is grounded.

[0050] The output terminal of the operational amplifier 1012 is connected to the input terminal of the current mixer 2:

[0051] The gate of the second NMOS transistor NM21 serves as the input terminal of the mirror current generation branch 201, and the input terminal of the mirror current generation branch 201 is the input terminal of the current mixer 2, that is, the gate of the second NMOS transistor NM21 is the input terminal of the current mixer 2.

[0052] The negative input terminal of the operational amplifier 1012 is connected to the drain of the first NMOS transistor NM11, and the negative output terminal of the operational amplifier 1012 is connected to the gate of the first NMOS transistor NM11 to ensure a negative feedback loop; through this connection relationship, a current mirror loop is realized, which can ensure that the current flowing through the first NMOS transistor NM11 can be accurately copied into the mirror current generation branch 201, that is, copied into the second NMOS transistor NM21.

[0053] If the device size parameters of the second NMOS transistor NM21 are exactly the same as those of the first NMOS transistor NM11, the current will be copied 1:1, that is, the negative signal of the reference current signal output by the first NMOS transistor NM11 is I S_IN then the current output by the second NMOS transistor NM21 is 1*I S_IN .

[0054] If the ratio of the device size parameters of the second NMOS transistor NM21 to those of the first NMOS transistor NM11 is 1:N, the current will be copied 1:N, that is, the negative signal of the reference current signal output by the first NMOS transistor NM11 is I S_IN then the current output by the second NMOS transistor NM21 is N*I S_IN ; The purpose of using the operational amplifier 1012 to achieve negative feedback is to increase the loop gain to reduce Figure 3 the impedance at point A in A so that, under the same current signal input, the swing of the voltage VA at point A is lower, and the first NMOS transistor NM11 has better linear performance.

[0055] The gate of the second NMOS transistor NM21 is connected to the negative output terminal of the operational amplifier 1012, that is, the gate of the second NMOS transistor NM21 is connected to the negative signal I of the reference current signal S_INConnect; the source of the second NMOS transistor NM21 is grounded; the sources of the third NMOS transistor NM25 and the fourth NMOS transistor NM26 are respectively connected to the drain of the second NMOS transistor NM21; the gates of the third NMOS transistor NM25 and the fourth NMOS transistor NM26 are respectively connected to the local oscillator, that is, the gate of the third NMOS transistor NM25 is connected to the negative signal LO- of the local oscillator signal, and the gate of the fourth NMOS transistor NM26 is connected to the positive signal LO+ of the local oscillator signal.

[0056] The output end of the mixing unit 202 is connected to the input end of the power amplifier 3:

[0057] The drains of the third NMOS transistor NM25 and the fourth NMOS transistor NM26 serve as the output end of the mixing unit 202, and the sources of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 serve as the input end of the power amplifier 3; the source of the fifth NMOS transistor NM31 is connected to the drain of the third NMOS transistor NM25; the source of the sixth NMOS transistor NM32 is connected to the drain of the fourth NMOS transistor NM26; the gates of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 are respectively connected to the bias voltage V BN connected to make the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 operate in the common-gate amplification state; the gates of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 are respectively connected to the balun module 4, so that the balun module 4 converts the current signal I output in a differential manner by the power amplifier 3 out2 into an output voltage V output in a single-ended manner out .

[0058] In the positive signal processing circuit when the baseband voltage signal V BB is the I-channel:

[0059] The baseband signal input branch 1011 includes a second resistor R12; the reference current output branch 1013 includes a seventh NMOS transistor NM12; the mirror current generation branch 201 includes an eighth NMOS transistor NM22; the mixing unit 202 includes a ninth NMOS transistor NM23 and a tenth NMOS transistor NM24; the power amplifier 3 includes a fifth NMOS transistor NM31 and a sixth NMOS transistor NM32.

[0060] The first end of the second resistor R12 is connected to the positive signal V of the baseband voltage signal BB_IP ; the second end of the second resistor R12 is connected to the positive input end of the operational amplifier 1012, that is, the positive input end of the operational amplifier 1012 is connected to the positive signal V of the baseband voltage signal BB_IPConnection; the drain of the seventh NMOS transistor NM12 is connected to the positive input terminal of the operational amplifier 1012; the gate of the seventh NMOS transistor NM12 is connected to the positive output terminal of the operational amplifier 1012, that is, the gate of the seventh NMOS transistor NM12 is connected to the positive signal I of the reference current signal S_IP Connection; the source of the seventh NMOS transistor NM12 is grounded.

[0061] The output terminal of the operational amplifier 1012 is connected to the input terminal of the current mixer 2:

[0062] The gate of the eighth NMOS transistor NM22 serves as the input terminal of the mirror current generation branch 201, and the input terminal of the mirror current generation branch 201 is the input terminal of the current mixer 2, that is, the gate of the eighth NMOS transistor NM22 is the input terminal of the current mixer 2.

[0063] The positive input terminal of the operational amplifier 1012 is connected to the drain of the seventh NMOS transistor NM12, and the positive output terminal of the operational amplifier 1012 is connected to the gate of the seventh NMOS transistor NM12 to ensure a negative feedback loop; through this connection relationship, a current mirror loop is realized, which can ensure that the current flowing through the seventh NMOS transistor NM12 can be accurately copied into the mirror current generation branch 201, that is, copied into the eighth NMOS transistor NM22.

[0064] If the device size parameters of the eighth NMOS transistor NM22 are exactly the same as those of the seventh NMOS transistor NM12, the current will be copied 1:1, that is, the positive signal of the reference current signal output by the seventh NMOS transistor NM12 is I S_IP then the current output by the eighth NMOS transistor NM22 is 1*I S_IP 。

[0065] If the ratio of the device size parameters of the eighth NMOS transistor NM22 to those of the seventh NMOS transistor NM12 is 1:N, the current will be copied 1:N, that is, the positive signal of the reference current signal output by the seventh NMOS transistor NM12 is I S_IP then the current output by the eighth NMOS transistor NM22 is N*I S_IP ; The purpose of using the operational amplifier 1012 to achieve negative feedback is to increase the loop gain to reduce Figure 3 the impedance at point B in B so that, under the same current signal input, the swing of the voltage V at point B is lower, making the second NMOS transistor NM12 have better linear performance.

[0066] The gate of the eighth NMOS transistor NM22 is connected to the positive output terminal of the operational amplifier 1012, that is, the gate of the eighth NMOS transistor NM22 is connected to the positive signal I of the reference current signal S_IPConnect; the source of the eighth NMOS transistor NM22 is grounded; the sources of the ninth NMOS transistor NM23 and the tenth NMOS transistor NM24 are respectively connected to the drain of the eighth NMOS transistor NM22; the gates of the ninth NMOS transistor NM23 and the tenth NMOS transistor NM24 are respectively connected to the local oscillator, that is, the gate of the ninth NMOS transistor NM23 is connected to the positive signal LO+ of the local oscillator signal, and the gate of the tenth NMOS transistor NM24 is connected to the negative signal LO- of the local oscillator signal.

[0067] The output end of the mixing unit 202 is connected to the input end of the power amplifier 3:

[0068] The drains of the ninth NMOS transistor NM23 and the tenth NMOS transistor NM24 serve as the output end of the mixing unit 202, and the sources of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 serve as the input end of the power amplifier 3; the source of the fifth NMOS transistor NM31 is connected to the drain of the ninth NMOS transistor NM23; the source of the sixth NMOS transistor NM32 is connected to the drain of the tenth NMOS transistor NM24; the gates of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 are respectively connected to the bias voltage V BN Connected to make the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 operate in the common-gate amplification state; the gates of the fifth NMOS transistor NM31 and the sixth NMOS transistor NM32 are respectively connected to the balun module 4, so that the balun module 4 converts the current signal I output in differential form by the power amplifier 3 out2 Into an output voltage V output in single-ended form out .

[0069] The operational amplifier 1012 designed by the present invention has a stable input common-mode ability, which can clamp the positive and negative input DC point potentials (point A and point B) of the operational amplifier 1012 at the common-mode voltage V CM Level; when the common-mode amplification factor of the operational amplifier 1012 is sufficient, it can ensure that the voltage V at point A A And the voltage V at point B B Are equal to the common-mode voltage V CM (V A = V B = V CM ).

[0070] Stable input common mode can also realize converting the baseband voltage signal V BB Into a reference current signal I S ; It can also realize stabilizing the common-mode levels of point A and point B, avoiding DC offset caused by layout mismatch between the first NMOS transistor NM11 and the seventh NMOS transistor NM12. Usually, this offset is positively correlated with the leakage energy of the transmitted local oscillator.

[0071] By using the input common-mode feedback clamping effect of the operational amplifier 1012, the input common mode of the current-mode mixer 2 is stabilized above a given common-mode level, avoiding the leakage of the local oscillator due to DC offset in traditional receivers.

[0072] For the convenience of analyzing the circuit performance, Figure 4 a simplified half-side equivalent circuit diagram is shown. For the negative signal processing circuit when the baseband voltage signal V BB is the negative signal of the I channel. Since the power amplifier 3 also includes a positive signal processing circuit and a negative signal processing circuit, only the half-side equivalent circuit of the power amplifier 3 (the negative signal processing circuit, that is, the output end of the balun module 4 is the grounded end) is shown in Figure 4 for analysis. The following formula can be obtained: Figure 4 For the analysis, the following formula can be obtained:

[0073] Baseband voltage signal to reference current signal:

[0074] Formula 1

[0075] Wherein, is the negative signal of the baseband voltage signal, and it can be considered as a voltage signal added on a common-mode voltage ; the voltage at point A is clamped at the common-mode voltage by the input of the operational amplifier; therefore, its relationship with the negative signal of the reference current signal is as shown in Formula 1. is as shown in Formula 1.

[0076] Input impedance at point A:

[0077] Formula 2

[0078] Wherein, is the amplification factor of the operational amplifier 1012, is the small-signal transconductance of the first NMOS transistor NM11; when the gate-drain of the operational amplifier 1012 is not shorted, the input impedance of the first NMOS transistor NM11 is , and after adding the operational amplifier 1012, the input impedance at point A is reduced by A times, as shown in Formula 2; generally, the large-signal swing from the previous-stage amplifier may be close to the full swing, that is, the voltage at point A with the same current has a swing reduced by A times, and the nonlinearity at point A will be significantly improved.

[0079] Overall transmit gain:

[0080] Formula 3

[0081] Wherein, N is the device size parameter ratio of the second NMOS transistor NM21 to the first NMOS transistor NM11; usually, the W and L sizes of the second NMOS transistor NM21 and the first NMOS transistor NM11 are the same, and the device quantity ratio of the former to the latter is N times; is the up-conversion gain of the mixer unit 202 ( Figure 4 in D); is the load impedance seen by the power amplifier 3 when the primary-secondary ratio of the balun module 4 is 1:1.

[0082] DC offset:

[0083] When the negative feedback of the operational amplifier 1012 is not used, the voltage at point A and the voltage at point B in the DC voltage representation (Formula 4), it can be seen that with the change of process and current, the voltages at these two points change violently.

[0084]

[0085] Formula 4

[0086] Wherein, is Figure 3 the branch current of the drain of the first NMOS transistor NM11 or the drain of the second NMOS transistor NM12 in , which changes with the input of the baseband voltage signal; β is considered to be related to the parameters in the process fabrication. When the first NMOS transistor NM11 and the second NMOS transistor NM12 are close in layout in the same wafer, it is considered that the deviation is small and can be considered not to change; and

[0087] are the device size and process parameters respectively, and there will be a large deviation in the layout design and production manufacturing, that is, there is a certain deviation. Figure 3 As shown in after the operational amplifier 1012 of the present invention is used to achieve common-mode clamping, the voltage at point A and the voltage at point B CM will be fixed at the common-mode voltage V

[0088] level by the gain of the operational amplifier 1012, and will no longer be affected by process and layout mismatch, that is:

[0089] At this time, since the DC levels at point A and point B are clamped, the DC offset at these two points is eliminated, and the emission carrier leakage caused by the DC offset is also reduced.

[0090] From the above analysis, it can be seen that the negative signal of the baseband voltage signal Negative signal converted into reference current signal After that, it will run through the entire transmission process and only be converted back to voltage gain output at the load end of the balun module 4; this can avoid the non-linear components brought by NMOS devices, especially the NMOS tubes in the mixer unit 202, during the transmission of large-signal voltages, improve the quality of the transmitted signal, and enable a higher saturated output power.

[0091] For the positive signal processing circuit when the baseband voltage signal V BB is for the I channel, the positive signal processing circuit when the baseband voltage signal V BB is for the Q channel, and the analysis process of the negative signal processing circuit when the baseband voltage signal V BB is for the Q channel, the analysis process can refer to the analysis process of the Figure 4 shown negative signal processing circuit when the baseband voltage signal V BB is for the I channel, and their analysis processes are the same.

[0092] Compared with the traditional transmitter front-end circuit, in the present invention, by adding a baseband signal converter 1 at the input end of the mixer, the baseband signal is converted from a voltage type to a current type, so that the input end of the mixer is a circuit signal; compared with the traditional mixer, the current-mode mixer 2 has better linear performance because it does not transmit voltage; it can be seen from the above formula 3 that the transmitter front-end circuit is current amplification throughout the entire process of mixing and amplification, and only switches back to voltage gain at the output end.

[0093] And an operational amplifier 1012 is added to the baseband signal converter 1 to form a negative feedback amplification loop, further reducing the impedance at the transconductance input end; it can be seen from the above formula 2 that Figure 4 the output impedance at point A in

[0094] is reduced by A times, which is beneficial to maintaining linearity when receiving a large-signal current input; CM In the design of the operational amplifier 1012, an input common-mode stabilization circuit is used to ensure that the common-mode voltage V

[0095] of the differential input of the baseband signal converter 1 is consistent with the set reference voltage (formula 5), and is not affected by the mismatch of the NMOS tubes in the mirror generation branch, suppressing the carrier leakage energy caused by DC offset.

[0096] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A current-mode transmitter front-end circuit, characterized in that Comprising: A baseband signal converter, a current-mode mixer, a power amplifier, and a balun module; The baseband signal converter is connected to the power amplifier through the current-mode mixer, and the power amplifier is connected to the balun module; The baseband signal converter is used to convert a plurality of input baseband voltage signals into a plurality of reference current signals for output; the current-mode mixer mixes the plurality of reference current signals with a local oscillator signal to generate a radio frequency current signal; the power amplifier is used to amplify the radio frequency current signal for output; the balun module is used to convert the radio frequency current signal output by the power amplifier into an output voltage and convert the differential output into a single-ended output; The baseband signal converter includes a plurality of conversion units; each conversion unit includes an operational amplifier, the input end of the operational amplifier is connected to a common-mode voltage, and the common-mode voltage is used to clamp the input signal of the operational amplifier at the same level as the common-mode voltage; the output end of the operational amplifier is connected to the input end of the current-mode mixer.

2. The current-mode transmitter front-end circuit according to claim 1, characterized in that Each conversion unit further includes a baseband signal input branch and a reference current output branch; The input end of the baseband signal input branch is connected to the baseband voltage signal; the input end of the operational amplifier is connected to the output end of the baseband signal input branch, the input end of the reference current output branch, and a supply voltage; the output end of the operational amplifier is connected to the output end of the reference current output branch.

3. The current-mode transmitter front-end circuit according to claim 2, wherein The baseband signal input branch includes a first resistor; The first end of the first resistor is connected to the baseband voltage signal; the second end of the first resistor is connected to the input end of the operational amplifier.

4. The current-mode transmitter front-end circuit according to claim 3, wherein The reference current output branch includes a first NMOS transistor; The drain of the first NMOS transistor is connected to the input end of the operational amplifier; the gate of the first NMOS transistor is connected to the output end of the operational amplifier; the source of the first NMOS transistor is grounded.

5. The front-end circuit of a current-mode transmitter according to claim 4, characterized in that The current-mode mixer includes a plurality of mirror current generation branches and a plurality of mixing units; The input end of the mirror current generation branch is connected to the output end of the operational amplifier; the output end of the mirror current generation branch is connected to the input end of the mixing unit; the input end of the mixing unit is connected to a local oscillator, and the local oscillator is used to provide the local oscillator signal; The output end of the mixing unit is connected to the input end of the power amplifier.

6. The current-mode transmitter front-end circuit according to claim 5, characterized in that The mirror current generation branch includes a second NMOS transistor; The gate of the second NMOS transistor is connected to the output end of the operational amplifier; the drain of the second NMOS transistor is connected to the input end of the mixing unit; the source of the second NMOS transistor is grounded.

7. The current-mode transmitter front-end circuit according to claim 6, wherein The mixing unit includes a third NMOS transistor and a fourth NMOS transistor; The source of the third NMOS transistor and the source of the fourth NMOS transistor are respectively connected to the drain of the second NMOS transistor; the drain of the third NMOS transistor and the drain of the fourth NMOS transistor are respectively connected to the input end of the power amplifier; the gate of the third NMOS transistor and the gate of the fourth NMOS transistor are respectively connected to the local oscillator.

8. The current-mode transmitter front-end circuit according to claim 7, characterized in that, The power amplifier includes a fifth NMOS transistor and a sixth NMOS transistor; The source of the fifth NMOS transistor is connected to the drain of the third NMOS transistor; the source of the sixth NMOS transistor is connected to the drain of the fourth NMOS transistor; the gate of the fifth NMOS transistor and the gate of the sixth NMOS transistor are respectively connected to the balun module; the gate of the fifth NMOS transistor and the gate of the sixth NMOS transistor are respectively connected to the bias voltage.

9. A transmitting system, characterized in that, It includes the current-mode transmitter front-end circuit according to any one of claims 1-8 above.

Images