N-Channel Filter-Based Single-Ended to Differential Signal Converter

Abstract

A single-ended to differential signal converter, using an N-channel filter for conversion. Specifically, the single-ended to differential signal converter includes an N-channel filter, the N-channel filter includes a plurality of channels, each of which includes a low-pass filter circuit, the low-pass filter circuit is selectively connected to the input port of the converter, selectively connected to the first output port of the converter to generate a first output signal, and selectively connected to the second output port of the converter to generate a second signal that is 180 degrees offset from the first output signal. In this way, the first and second output signals form a differential signal pair corresponding to the single-ended input signal.

Description

Technical Field

[0001] The present application relates to electronic circuits and, more particularly, to single-ended to differential signal converters. Background Art

[0002] A wireless receiver receives a single-ended signal and usually converts the received single-ended signal into a differential signal (i.e., a differential signal pair) for processing. It is usually advantageous to convert the received single-ended signal into a differential signal (i.e., a differential signal pair) as early as possible because the differential interface can suppress external interfering noise, suppress even-order distortion components (this is very important in a direct conversion receiver because even-order components in low-frequency signals are difficult to filter out), and improve gain (because the output voltage can be twice that of a single-ended signal).

[0003] There are many known techniques for converting single-ended signals to differential signals, but many suffer from one or more of the following factors: asymmetry, expensive area, noise, linearity, and high power consumption.

[0004] For example, a common technique for converting a single-ended signal to a differential signal is to use one or more on-chip inductor baluns. As known to those skilled in the art, an inductor balun is a circuit that uses one or more inductors to convert a single-ended signal to a differential signal. The area cost of an on-chip inductor balun is generally high. In addition, because the on-chip inductor balun is very narrow-band, multiple inductors are often used to provide coverage for broadband operation. The receiver typically includes a gain stage, such as a low-noise amplifier (LNA). Figure 1 and Figure 2 As shown, the inductor balun 102, 202 can be placed before or after the gain stage 104, 204. Figure 1 As shown, if the inductor balun 102 is placed before the gain stage (e.g., LNA) 104, the output of the LNA 104 will be fully differential and will benefit from reduced even-order distortion components at its output. This helps to set the input matching conditions in a simple and clear manner. However, placing the inductor balun 102 before the gain stage 104 may have an adverse effect on the noise figure and may require special attention to any local oscillator (LO) leakage. Conversely, if Figure 2 As shown, the inductor balun 202 is placed after the gain stage (eg, LNA) 204 , and the inductor balun 202 cannot correct any nonlinearity introduced by the gain stage (eg, LNA) 204 .

[0005] Another common technique for converting a single-ended signal to a differential signal is to use an active balun. While most baluns include passive components, such as an inductor, an active balun includes an amplification device. Therefore, an active balun can be integrated with a gain stage (e.g., an LNA). Figure 3 and Figure 4 Two exemplary implementations of an active balun integrated into an LNA are shown. Figure 3 shows a resistor-feedback inverter differential LNA, Figure 4 A cascode differential LNA is shown. Active baluns are advantageous over inductive baluns because they are inherently broadband, can be implemented in a very small area, and can nearly double the amplitude of the output signal. However, since they have active components, they are power hungry. It is also difficult to obtain a symmetrical, fully differential signal from two parts of a circuit that is not functionally symmetrical. Such active baluns are also prone to signal noise and nonlinearity.

[0006] The embodiments described below are provided by way of example only and are not intended to limit implementations that address any or all of the disadvantages of known single-ended to differential signal converters. Summary of the invention

[0007] This summary is intended to introduce some concepts that will be further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0008] This article describes a single-ended to differential signal converter that uses an N-channel filter for conversion. Specifically, the single-ended to differential signal converter includes an N-channel filter, the N-channel filter includes a plurality of channels, each of which includes a low-pass filter circuit, the low-pass filter circuit is selectively connected to the input port of the converter, selectively connected to the first output port of the converter to generate a first output signal, and selectively connected to the second output port of the converter to generate a second signal that is 180 degrees offset from the first output signal. In this way, the first and second output signals form a differential signal pair corresponding to the single-ended input signal.

[0009] In a first aspect, a single-ended to differential signal converter is provided, comprising: an input port for receiving a single-ended signal; a first output port for outputting a first signal in a differential signal pair; a second output port for outputting a second signal in the differential signal pair; and an N-channel filter comprising a plurality of channels, each channel comprising a low-pass filter circuit, the low-pass filter circuit being selectively connected to the input port, selectively connected to the first output port, and selectively connected to the second output port.

[0010] This single-ended to differential signal converter has a negligible effect on noise and does not consume any additional DC power. In addition, the N-channel filter can also be used in a wireless receiver to perform baseband filtering. Therefore, since converting a single-ended N-channel filter to a single-ended to differential converter requires only the addition of one (or two) switches in each channel, the increase in size and complexity of the receiver chip is negligible.

[0011] Each channel may also include: a first switching circuit, which, when activated, connects the first output port to the low-pass filtering circuit; and a second switching circuit, which, when activated, connects the second output port to the low-pass filtering circuit; wherein the first switching circuit is activated by a first control signal and the second switching circuit is activated by a second control signal that is offset from the first control signal.

[0012] Each channel may further include a third switching circuit that, when activated, connects the input port to the low-pass filtering circuit.

[0013] The first switching circuits of the plurality of channels may be activated in sequence, and the third switching circuits of the plurality of channels may be activated in the same sequence.

[0014] The third switching circuit of one channel may be activated by a third control signal having a different phase from the first and second control signals.

[0015] The phase of the third control signal may differ from the phase of one of the first and second control signals by 360 / n, where n is the number of channels in the N-channel filter.

[0016] The third switching circuit of one channel and the first or second switching circuit of another channel may be activated by the same control signal.

[0017] The input port may be short-connected to the first output port such that when the first switch of a channel is activated, the input port and the first output port are connected to the low pass filter circuit of the channel.

[0018] The first switching circuit of one channel and the second switching circuit of another channel may be activated by the same control signal.

[0019] The first switching circuit of at least one channel may include a single switch.

[0020] The second switching circuit of at least one channel may include a single switch.

[0021] When a low-pass filter circuit is connected to the input port at the same frequency as the single-ended signal, the low-pass filter circuit may receive a baseband version of the single-ended signal, which is converted by the low-pass filter circuit into a filtered baseband signal.

[0022] When a control signal having the same frequency as the single-ended signal activates the first switching circuit, the first switching circuit may up-convert the filtered baseband signal to an original frequency band of the single-ended signal.

[0023] When a control signal having the same frequency as the single-ended signal activates the second switching circuit, the second switching circuit may up-convert the filtered baseband signal to an original frequency band of the single-ended signal.

[0024] The single-ended signal may be a radio frequency signal.

[0025] The first and second signals of the differential signal pair may be radio frequency signals.

[0026] The at least one low pass filter circuit may include a capacitor in parallel with a resistor.

[0027] The second aspect provides a front-end signal processing circuit, comprising: an amplifier for outputting a single-ended signal; and the single-ended to differential signal converter of the first aspect, wherein the input port of the single-ended to differential signal converter is coupled to the output port of the amplifier.

[0028] A third aspect provides a method for converting a single-ended input signal into a differential signal pair, comprising: connecting the single-ended input signal to multiple low-pass filter circuits in sequence; generating a first signal of the differential signal pair by sequentially outputting the signal generated by the low-pass filter circuit via a first switching circuit associated with the low-pass filter circuit; and generating a second signal of the differential signal pair by sequentially outputting a signal generated by one of the low-pass filter circuits via a second switching circuit associated with the low-pass filter circuit; wherein the first and second signals in the differential signal pair include signals generated by the same low-pass filter circuit during a phase offset period.

[0029] The above features may be combined as appropriate, as will be apparent to the skilled person, and may be combined with any aspects of the examples described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Examples will now be described in detail with reference to the accompanying drawings, in which:

[0031] Figure 1 is a block diagram of a circuit consisting of an inductor balun and a differential LNA;

[0032] Figure 2It is a block diagram of the circuit consisting of LNA and inductor balun;

[0033] Figure 3 is a circuit diagram of a first example circuit implementing an active balun;

[0034] Figure 4 is a circuit diagram of a second example circuit implementing an active balun;

[0035] Figure 5 is a circuit diagram of an example single-ended N-channel filter;

[0036] Figure 6 yes Figure 5 A timing diagram of example control signals for a single-ended N-channel filter;

[0037] Figure 7 is a circuit diagram of an example differential N-channel filter;

[0038] Figure 8 is a circuit diagram of a first example single-ended to differential signal converter including an N-channel filter;

[0039] Fig. 9 is a circuit diagram of a second example single-ended to differential signal converter including an N-channel filter;

[0040] Fig.10 is shown including the LNA and the subsequent Fig. 9 A graph of a front end circuit of a single-ended to differential signal converter and a frequency response of the front end circuit including an LNA and a subsequent single-ended N-channel filter; and

[0041] Fig.11 is a flow chart of an example method for converting a single-ended signal to a differential signal pair.

[0042] The accompanying drawings show various examples. It will be appreciated by the skilled person that the element boundaries (e.g., boxes, boxes groups, or other shapes) shown in the accompanying drawings represent one example of boundaries. In some examples, one element may be designed as multiple elements, or multiple elements may be designed as one element. Common reference numerals are used throughout the accompanying drawings as appropriate to represent similar features. DETAILED DESCRIPTION

[0043] The following description is by way of example only to enable those skilled in the art to make and use the invention. The invention is not limited to the embodiments described herein, and various modifications to the disclosed embodiments will be apparent to those skilled in the art. The embodiments are described by way of example only.

[0044] Described herein is a single-ended to differential signal converter that generates a differential signal (ie, a differential signal pair) from a single-ended input signal using a single-ended N-channel filter.

[0045] An N-channel filter (also referred to as a channel selection filter) includes N identical parallel signal channels, where N is an integer greater than or equal to 2. Each channel includes: an input modulator that downconverts the input signal to baseband; a low-pass filter circuit that filters the baseband signal to generate a filtered baseband signal; and an output modulator that upconverts the filtered baseband signal to the original frequency band of the input signal. At any given time, the low-pass filter circuit is connected between the input and output through a single channel. The low-pass filtering performed at the baseband is converted into bandpass filtering once upconverted. The center frequency of the filter is determined by the mixing frequency. It has been demonstrated that N-channel filters can provide bandpass filters with high Q factors and wide center frequency tuning ranges.

[0046] Reference Figure 5-Figure 7 , which shows the characteristics of an N-channel filter. Figure 5 An example of a single-ended N-channel filter 500 is shown, which receives a single-ended input signal and generates a single-ended output signal, which is a filtered version of the input signal. The single-ended N-channel filter 500 includes an input port 502 for receiving a single-ended input signal (V_IN) and an output port 504 for outputting a filtered version of the input signal (V_OUT). In some cases, the single-ended input signal (V_IN) and the single-ended output signal (V_OUT) are radio frequency signals (RF). However, in other cases, the input signal (V_IN) and the output signal (V_OUT) can be in different frequency bands.

[0047] The N-channel filter 500 also includes N identical signal channels 506-1 to 506-N, where N is an integer greater than or equal to 2. Common values ​​of N are 4 and 8, but it is obvious to those skilled in the art that these are only examples and other values ​​of N can be used. Each channel 506-i includes a low-pass filter circuit (R+Ci) and a switching circuit (Si) connected in series. Figure 5 In the example shown, each low-pass filter circuit is composed of a capacitor Ci and a resistor R (representing the resistance between the input voltage source and the input port 502). However, it is obvious to those skilled in the art that this is only an example low-pass filter circuit, and other low-pass filter circuits can be used. Figure 5 In the example shown, each switching circuit includes a single switch Si, however, in other examples, one or more switching circuits may include more than one switch.

[0048] The switching circuit (Si) of channel i is located between the input port and the corresponding low-pass filter circuit, so that when the switching circuit (Si) is activated (i.e., closed), the input port 502 is connected to the corresponding low-pass filter circuit (R+Ci). Figure 5 The N-channel filter 500 of the embodiment of the present invention is shorted, and the activation of the switching circuit (Si) also connects the output port 504 to the corresponding low-pass filtering circuit (R+Ci). In this configuration, the switching circuit (Si) of the periodically activated channel i down-converts the input signal to baseband, the low-pass filtering circuit (R+Ci) filters the baseband signal to generate a filtered baseband signal, and the same switching circuit (Si) up-converts the filtered baseband signal to the original frequency band of the input signal provided to the output port 504. The components of the low-pass filtering circuit (e.g., C1, C2, ... CN) are selected to provide the desired channel filtering according to the input signal bandwidth.

[0049] Typically, the switching circuits (S1, S2, ... SN) are activated in sequence so that only one switching circuit (Si) is effective at a time, and the effective time of each switching circuit (S1, S2, ... SN) is the same. For example, the switching circuits can be activated in the order of S1, S2, ... SN. In some cases, each switching circuit (Si) is activated by a corresponding control signal (Pi). Specifically, the control signal P1 controls the activation of the first switching circuit (S1), the control signal P2 controls the activation of the second switching circuit (S2), and so on. In some cases, the control signal is based on the LO signal.

[0050] Figure 6 Shown for Figure 5 An example set of control signals (P1, P2, ... PN) for the N-channel filter 500, wherein each control signal represents a phase-shifted version of the LO signal. Specifically, the i-th control signal Pi represents a (i-1)*360 / N) degree phase-shifted version of the LO signal. For example, in the case of N=4, there will be four control signals (P1, P2, P3, and P4), wherein P1 represents a 0 degree phase-shifted version of the LO signal, P2 represents a 90 degree phase-shifted version of the LO signal, P3 represents a 180 degree phase-shifted version of the LO signal, and P4 represents a 270 degree phase-shifted version of the LO signal. In this example, each control signal has a duty cycle equal to 1 / N of the LO period (T_LO). This results in each switching circuit (Si) being activated at 1 / N of the LO period. The LO signal can be set to the center frequency of the input signal so that Figure 5 The N-channel filter 500 is well suited for direct conversion receivers.

[0051] The low-pass filtering performed by the plurality of channels 506 - 1 to 506 -N at the baseband is converted to a band-pass filtering effect after up-conversion.

[0052] Figure 7 An example differential N-channel filter 700 is shown. Figure 7 The differential N-channel filter 700 receives a differential signal pair as input and outputs a differential signal pair representing filtered versions of the input signals. Figure 7 The differential N-channel filter 700 and Figure 5 The single-ended N-channel filter 500 is similar to the single-ended N-channel filter 500, except that it does not include a single input port and a single output port, but includes two input ports 702, 703 and two output ports 704, 705. Each input port 702, 703 receives one signal in the differential signal pair, and each output port 704, 705 outputs one signal in the differential signal pair. In addition, each channel 706-1 to 706-4 does not include a single switching circuit that connects the input port and the output port to the corresponding low-pass filter, but includes two switching circuits S1-1 to S4-1 and S1-2 to S4-2. Specifically, each channel 706-i includes: a first switching circuit Si-1, which, when activated, connects the first input port 702 and the first output port 704 to the corresponding low-pass filter circuit (Ci+R / 2); and a second switching circuit Si-2, which, when activated, connects the second input port 703 and the second output port 705 to the corresponding low-pass filter circuit (Ci+R / 2). The first and second switching circuits Si-1 and Si-2 of channel i are controlled by control signals that are out of phase with each other (ie, each control signal represents a 180 degree phase shifted version of the other control signal).

[0053] For example, if the first switching circuits S1-1 to S4-1 are activated by control signals representing 0, 90, 180, and 270 degree phase shifted versions of the LO signal, the second switching circuits S1-2 to S4-2 are activated by control signals representing 180, 270, 0, and 90 degree phase shifted versions of the LO signal as shown in Table 1. This means that the control signal used to control the first switching circuit can be multiplexed to control the second switching circuit. For example, the control signal used to control the first switching circuit of the first channel S1-1 can also be used to control the second switching circuit of the third channel S3-2, and the control signal used to control the first switching circuit of the second channel S2-1 can also be used to control the second switching circuit of the fourth channel S4-2, and so on.

[0054] Table 1

[0055]

[0056] However, Figure 7 The differential N-channel filter requires differential inputs.

[0057] Described herein is a single-ended to differential signal converter that generates a differential signal (i.e., a differential signal pair) from a single-ended input signal using a single-ended N-channel filter. The differential signal is generated by selectively connecting an input port of the N-channel filter to each low-pass filter circuit, selectively connecting the low-pass filter circuit to a first output port to generate a first output signal, and selectively connecting the low-pass filter circuit to a second output port to generate a second output signal, such that the second output signal is 180 degrees offset from the first output signal. In this manner, the first and second output signals form a differential signal pair that represents a filtered version of the single-ended input signal.

[0058] This can be achieved by adding one or more switching circuits in each channel of the single-ended N-channel filter. For example, in one exemplary embodiment, each channel has a first switching circuit (e.g., Figure 5 The N-channel filter 500 may include a first switching circuit (S1 to SN) that, when activated, connects the input port and the first output port to the corresponding low-pass filter circuit; and a second switching circuit that, when activated, connects the corresponding low-pass filter circuit to the second output port. In another exemplary embodiment, each channel may have a first switching circuit that, when activated, connects the input port to the corresponding low-pass filter circuit; a second switching circuit that, when activated, connects the corresponding low-pass filter circuit to the first output port; and a third switching circuit that, when activated, connects the corresponding low-pass filter circuit to the second output port. In either case, the switches of the same channel that connect the low-pass filter circuit to the first and second output ports, respectively, are activated by anti-phase control signals (i.e., each control signal represents a 180-degree phase shift of the other control signal).

[0059] This single-ended to differential signal converter has a negligible effect on noise and does not consume any additional DC power. In addition, because of the desire to implement low-cost tunable filtering, many wireless receivers can include N-channel filters to perform baseband filtering, which means that the increase in size and complexity of the receiver chip is negligible because only one (or two) additional switches are required in each channel when converting a single-ended N-channel filter to a single-ended to differential signal converter.

[0060] Reference Figure 8, which shows a first example single-ended to differential signal converter 800 including an N-channel filter. The single-ended to differential signal converter 800 includes an input port 802 for receiving a single-ended input signal (V_IN), a first output port 804 for outputting a first output signal (V_OUT_P) of a differential signal pair, and a second output port 805 for outputting a second output signal (V_OUT_N) of the differential signal pair. In this example, the input port 802 is shorted to the first output port 804. In contrast, the second output port 805 is not shorted to the input port 802. In some cases, the input and output signals may be RF signals, however, in other cases, the input and output signals may be in different frequency bands.

[0061] The single-ended to differential signal converter 800 also includes an N-channel filter having N channels 806-1 to 806-4. In this example, N=4. However, it is obvious to those skilled in the art that this is only an example, and N can be any integer greater than or equal to 2. Each channel 806-i of the N-channel filter includes a low-pass filter circuit 808-i, a first switching circuit 810-i, and a second switching circuit 812-i. Figure 8 In the example shown, each low-pass filter circuit 808-i is formed by a capacitor Ci and a resistor Ri in parallel. However, it is obvious to those skilled in the art that this is only an example of a low-pass filter circuit, and other low-pass filter circuits may also be used. Figure 8 In the example shown, each of the first and second switching circuits 810-i and 812-i includes a single switch Si-1 or Si-2, however, in other examples, one or more of the switching circuits 810-1 to 810-4, 812-1 to 812-4 may include more than one switch. The components of the low-pass filter circuit (e.g., R1-R4 and C1-C4) are selected to provide the desired channel filtering according to the input signal bandwidth.

[0062] Each first switching circuit 810-1 to 810-4 is located between the input port 802 (and the first output port 804) and the corresponding low-pass filter circuit 808-1 to 808-4, so that when the first switching circuit 810-i of channel i is activated (i.e., closed), the input port 802 and the first output port 804 are connected to the corresponding low-pass filter circuit 808-i. In this configuration, the periodic activation of the first switching circuit 810-i of channel i down-converts the input signal to baseband and provides the baseband signal to the low-pass filter circuit 808-i. The low-pass filter circuit 808-i generates a filtered baseband signal from the baseband signal. The first switching circuit 810-i then up-converts the filtered baseband signal to the original frequency band of the input signal and provides the up-converted signal to the first output port 804.

[0063] Each second switching circuit 812-1 to 812-4 is located between the second output port 805 and the corresponding low-pass filter circuit 808-1 to 808-4, so that when the second switching circuit 812-i of channel i is activated (i.e., closed), the second output port 805 is connected to the corresponding low-pass filter circuit 808-i. Figure 8 In the example shown, one end of each second switching circuit 812-i is connected to the second output port 805, and the other end of the second switching circuit 812-i is connected to the wire or trace between the corresponding first switching circuit 810-i and the corresponding low-pass filter circuit 808-i. When the second switching circuits 812-1 to 812-4 are located between the second output port 805 and the corresponding low-pass filter circuit 808-i, the periodic activation of the second switching circuit 812-i of channel i causes the second switching circuit 812-i to act as an up-converter. Specifically, the periodic activation of the second switching circuit 812-i up-converts the filtered baseband signal generated by the corresponding low-pass filter circuit 808-i to the original frequency band of the input signal, and provides the up-converted signal to the second output port 805.

[0064] In this arrangement, when the second switching circuit 812-i of channel i is activated (ie, closed), substantially no current will flow through the second switching circuit 812-i. Since substantially no current will flow through the second switching circuits 812-1 to 812-4, the switches of the second switching circuits 812-1 to 812-4 can be smaller than the switches of the first switching circuits 810-1 to 810-4. In some cases, the switches of the second switching circuits can be an order of magnitude smaller than the switches of the first switching circuits. The size of the switch can be the physical size of the switch, which can be defined by the length (L) and width (W) of the switch. For example, the size of the switch can be defined by the area of ​​the switch, which is equal to the product of the length and the width (LxW). In some cases, the minimum size of the switch of the second switching circuit can be limited by the maximum acceptable noise. For example, the switches of the second switching circuits 812-1 to 812-4 can be reduced to any size as long as their impact on the total noise is acceptable. Generally, the lower the frequency, the smaller the switch can be. Reducing the size of the switches of the second switching circuit can reduce the area for implementing the single-ended to differential signal converter 800 .

[0065] The first switching circuits 810-1 to 810-4 are activated in sequence so that only one first switching circuit 810-1 to 810-4 is effective at a time, and each first switching circuit 810-1 to 810-4 is effective for the same time. For example, the first switching circuits 810-1 to 810-4 can be activated in the order of 810-1, 810-2, 810-3, and 810-4. In some cases, each of the first switching circuits 810-1 to 810-4 is activated by a corresponding control signal, which is a phase-shifted version of the LO, wherein each control signal has a duty cycle equal to 1 / N of the LO period.

[0066] For example, the first switching circuits 810-1 to 810-4 may be composed of Figure 6 The exemplary control signals P0 to P4 shown respectively control Figure 2 In the example shown, the i-th control signal Pi represents a (i–1)*360 / N) degree phase shifted version of the LO signal. For example, in the case of N=4, there will be four control signals (P1, P2, P3, and P4), where P1 represents a 0 degree phase shifted version of the LO signal, P2 represents a 90 degree phase shifted version of the LO signal, P3 represents a 180 degree phase shifted version of the LO signal, and P4 represents a 270 degree phase shifted version of the LO signal. For those skilled in the art, this is obviously just an example, and the control signals of the first switching circuits 810-1 to 810-4 can represent different phase shifts of the LO signal, but they are usually separated by 360 / N degrees.

[0067] The second switching circuits 812-1 to 812-4 are activated in the same order as the corresponding first switching circuits 810-1 to 810-4. For example, if the first switching circuits 810-1 to 810-4 are activated in the order of 810-1, 810-2, 810-3, 810-4, the second switching circuits 812-1 to 812-4 are activated in the order of 812-1, 812-2, 812-3, 812-4. However, the second switching circuits 812-1 to 812-4 are activated with a phase difference of 180 degrees from the corresponding first switching circuits. Specifically, each second switching circuit 812-1 to 812-4 is activated by a control signal that is phase-shifted by 180 degrees, and the control signal is used to activate the corresponding first switching circuit. For example, when N is equal to 4, and the first switching circuits 810-1 to 810-4 are activated by control signals representing 0 degree, 90 degree, 180 degree and 270 degree phase-shifted versions of the LO signal, respectively, the corresponding second switching circuits 812-1 to 812-4 are activated by control signals representing 180 degree, 270 degree, 0 degree and 90 degree phase-shifted versions of the LO signal, as shown in Table 2.

[0068] Table 2

[0069]

[0070]

[0071] It will be apparent to one skilled in the art that these are exemplary phase shifts for the control signals and that other phase shifts may be used. For example, in another example, the first switching circuits 810-1 to 810-4 may be activated by control signals representing 5 degree, 95 degree, 185 degree, and 275 degree phase shifted versions of the LO signal, and the second switching circuits 812-1 to 812-4 may be activated by control signals representing 185 degree, 275 degree, 5 degree, and 95 degree phase shifted versions of the LO signal.

[0072] exist Figure 8An amplifier 820, such as an LNA, may be added before the converter 800 to form the front-end circuitry of the wireless receiver. Specifically, the amplifier (e.g., LNA) 820 may be used to receive a single-ended RF signal captured by an antenna, generate a single-ended amplified version of the received signal and provide it to the input port 802 of the converter 800. The output V_OUT (V_OUT_N and V_OUT_P) of the converter 800 may then be provided to a mixer and / or baseband processing component. By placing the amplifier (e.g., LNA) 820 before the converter 800, the amplifier may be impedance matched to the input circuit (e.g., antenna), thereby relaxing restrictions on the components of the converter 800 (e.g., relaxing restrictions on the components of the switching circuit and the low-pass filtering circuit). For example, in some cases, placing the amplifier (e.g., LNA) 820 before the converter relaxes restrictions on the size of the switch and the low-pass filtering circuit. In this configuration, it may be advantageous for the amplifier to have a high output impedance because this will allow the capacitor of the low-pass filtering circuit to be smaller. However, LNAs typically have low output impedance, which not only results in larger capacitors for the low-pass filter circuit, but also limits the amount of out-of-band rejection that can be achieved. While having a gain stage (e.g., amplifier) ​​before converter 800 may provide some advantages, it means that the gain stage (e.g., amplifier) ​​does not receive the filtered signal at its input (as would be the case if converter 800 was placed before the gain stage (e.g., amplifier)). As a result, the gain stage (e.g., amplifier) ​​exhibits the full strength of the out-of-band blocker, increasing the risk of saturation.

[0073] Figure 8 The single-ended to differential converter 800 can be generated from a single-ended N-channel filter by adding a single switching circuit on each channel without increasing the complexity of the control circuit (the circuit that generates the control signal that controls the activation of the switching circuit) because the same control signal used to activate the first switching circuit can be used to activate the additional switching circuit. However, since one of the output ports 804 is shorted to the input port 802 and the other output port 805 is not shorted to the input port 802, the driving capabilities of the two output ports 804 and 805 may be different. Accordingly, the first output signal and the second output signal (V_OUT_P and V_OUT_N) may be asymmetric. This may not be desirable for some applications, depending on how sensitive the downstream components (i.e., the components after the single-ended to differential signal converter) are to the asymmetry of the two signals forming the differential signal pair.

[0074] Accordingly, reference is now made to Fig. 9, which shows a second example single-ended to differential converter 900, in which the direct short circuit between the first output port and the input port is removed, and a third switching circuit is added to each channel, which, when activated, connects the first output port to the corresponding low-pass filter circuit. The single-ended to differential signal converter 900 includes an input port 902 for receiving a single-ended input signal (V_IN), a first output port 904 for outputting a first output signal (V_OUT_P) of a differential signal pair, and a second output port 905 for outputting a second output signal (V_OUT_N) of the differential signal pair. In this example, neither output port 904 nor 905 is shorted to input port 902.

[0075] The single-ended to differential signal converter 900 also includes an N-channel filter having N channels 906-1 to 906-4. In this example, N=4. However, it is obvious to those skilled in the art that this is only an example, and N can be any integer greater than or equal to 2. Each channel 906-i of the N-channel filter includes a low-pass filter circuit 908-i, a first switching circuit 910-i, a second switching circuit 912-i, and a third switching circuit 914-i. Fig. 9 In the example shown, each low-pass filter circuit 908-i is formed by a capacitor Ci and a resistor Ri in parallel. However, it is obvious to those skilled in the art that this is only an example of a low-pass filter circuit, and other low-pass filter circuits may also be used. Fig. 9 In the example shown, each of the first, second and third switching circuits 910-i, 912-i and 914-i includes a single switch Si-1, Si-2 or Si-3, however, in other examples, one or more of the switching circuits 910-1 to 910-4, 912-1 to 912-4 or 914-1 to 914-4 may include more than one switch. The components (e.g., R1-R4 and C1-C4) of the low-pass filter circuit are selected to provide the desired channel filtering according to the input signal bandwidth.

[0076] Each first switching circuit 910-1 to 910-4 is located between the input port 902 and the corresponding low-pass filter circuit 908-1 to 908-4, so that when the first switching circuit 910-i of channel i is activated (i.e., closed), the input port 902 is connected to the corresponding low-pass filter circuit 908-i. In this configuration, the periodic activation of the first switching circuit 910-i of channel i down-converts the input signal to baseband and provides the baseband signal to the low-pass filter circuit 908-i. The low-pass filter circuit 908-i then generates a filtered baseband signal from the baseband signal.

[0077] Each second switching circuit 912-1 to 912-4 is located between the second output port 905 and the corresponding low-pass filter circuit 908-1 to 908-4, so that when the second switching circuit 912-i of channel i is activated (i.e., closed), the second output port 905 is connected to the corresponding low-pass filter circuit 908-i. Fig. 9 In the example shown, one end of each second switching circuit 912-i is connected to the second output port 905, and the other end of the second switching circuit 912-i is connected to the wire or trace between the corresponding first switching circuit 910-i and the corresponding low-pass filter circuit 908-i. When the second switching circuits 912-1 to 912-4 are located between the second output port 905 and the corresponding low-pass filter circuit, the periodic activation of the second switching circuit 912-i of channel i up-converts the filtered baseband signal to the original frequency band of the input signal and provides the up-converted signal to the second output port 905.

[0078] Each third switching circuit 914-1 to 914-4 is located between the first output port 904 and the corresponding low-pass filter circuit 908-1 to 908-4, so that when the third switching circuit 914-i of channel i is activated (i.e., closed), the first output port 904 is connected to the corresponding low-pass filter circuit 908-i. Fig. 9 In the example shown, one end of each third switching circuit 914-i is connected to the first output port 904, and the other end of the second switching circuit 912-i is connected to the wire or trace between the corresponding first switching circuit 910-i and the corresponding low-pass filter circuit 908-i. When the third switching circuits 914-1 to 914-4 are located between the first output port 904 and the corresponding low-pass filter circuit, the periodic activation of the third switching circuit 914-i of channel i up-converts the filtered baseband signal generated by the corresponding low-pass filter circuit 908-i to the original frequency band of the input signal, and provides the up-converted signal to the first output port 904.

[0079] In this arrangement, when the second or third switching circuit 912-i or 914-i of channel i is activated (i.e., closed), substantially no current will flow through the second switching circuit 912-i or the third switching circuit 914-i. Since substantially no current will flow through the second and third switching circuits 912-1 to 912-4 and 914-1 to 914-4, the switches of the second and / or third switching circuits 912-1 to 912-4 and / or 914-1 to 914-4 can be smaller than the switches of the first switching circuits 910-1 to 910-4. In some cases, the switches of the second and third switching circuits can be an order of magnitude smaller than the switches of the first switching circuit. In some cases, the minimum size of the switches of the second and third switching circuits can be limited by the maximum acceptable noise. For example, the switches of the second and third switching circuits 912-1 to 912-4 and 914-1 to 914-4 can be reduced to any size as long as the maximum acceptable noise is achieved. Generally speaking, the lower the frequency, the smaller the switch can be.

[0080] In a single-ended N-channel filter (e.g., Figure 5 ), the on-resistance of the switching circuit is on the signal path, so current flows through it. Accordingly, in a single-ended N-channel filter, the on-resistance of the switching circuit can limit out-of-band suppression. However, since substantially no current flows through the second and third switching circuits 912-1 to 912-4 and 914-1 to 914-4, the on-resistance of the second and third switching circuits does not limit out-of-band suppression. Accordingly, reducing the size of the switches of the second switching circuit can reduce the area of ​​implementing a single-ended to differential signal converter and / or reduce the linearity requirements of downstream components connected to the output ports 904 and 905 of the converter 900.

[0081] The first switching circuits 910-1 to 910-4 are activated in sequence such that only one first switching circuit 910-1 to 910-4 is effective at a time and each first switching circuit 910-1 to 910-4 is effective for the same amount of time. For example, the first switching circuits 910-1 to 910-4 can be activated in the order of 910-1, 910-2, 910-3, and 910-4. In some cases, each of the first switching circuits 910-1 to 910-4 is activated by a corresponding control signal, which is a phase-shifted version of the LO, wherein each control signal has a duty cycle equal to 1 / N of the LO period. For example, the first switching circuits 910-1 to 910-4 can be activated by Figure 6 The exemplary control signals P0 to P4 shown respectively control Figure 6In the example shown, the i-th control signal Pi represents a (i–1)*360 / N) degree phase shifted version of the LO signal. For example, in the case of N=4, there will be four control signals (P1, P2, P3, and P4), where P1 represents a 0 degree phase shifted version of the LO signal, P2 represents a 90 degree phase shifted version of the LO signal, P3 represents a 180 degree phase shifted version of the LO signal, and P4 represents a 270 degree phase shifted version of the LO signal. For those skilled in the art, this is obviously just an example, and the control signals of the first switching circuits 910-1 to 910-4 can represent different phase shifts of the LO signal, but they are usually separated by 360 / N degrees.

[0082] The activation order of the second and third switching circuits 912-1 to 912-4 and 914-1 to 914-4 is the same as the activation order of the corresponding first switching circuits 910-1 to 910-4. For example, if the first switching circuits 910-1 to 910-4 are activated in the order of 910-1, 910-2, 910-3, 910-4, the second switching circuits 912-1 to 912-4 are activated in the order of 912-1, 912-2, 912-3, 912-4, and the third switching circuits 914-1 to 914-4 are activated in the order of 914-1, 914-2, 914-3, 914-4. However, the second and third switching circuits 912-1 to 912-4 and 914-1 to 914-4 are activated with a different phase offset from the corresponding first switching circuits and 180 degrees offset from each other. Specifically, each second switching circuit 912-1 to 912-4 is activated by a control signal with a phase shift of a predetermined amount, which is used to activate the corresponding first switching circuit; and is phase-shifted by 180 degrees relative to the control signal used to activate the corresponding third switching circuit.

[0083] For example, where N is equal to 4, when the first switching circuits 910-1 to 910-4 are activated by control signals representing 0 degree, 90 degree, 180 degree, and 270 degree phase-shifted versions of the LO signal, respectively, the second switching circuits 912-1 to 912-4 can be activated by control signals representing 270 degree, 0 degree, 90 degree, and 180 degree phase-shifted versions of the LO signal, respectively, and the third switching circuits 914-1 to 914-4 can be activated by control signals representing 90 degree, 180 degree, 270 degree, and 0 degree phase-shifted versions of the LO signal, respectively, as shown in Table 3.

[0084] Table 3

[0085]

[0086] It will be apparent to one skilled in the art that these are exemplary phase shifts of the control signals and that other phase shifts may be used. In particular, while it may be advantageous to correlate the control signal that activates / controls the first switching circuit with the control signal that activates the corresponding second or third switching circuit by a factor of 360 / N so that the same N control signals can be used to control all switching circuits, the control signal that activates / controls the first switching circuit may be correlated with the control signal that activates the corresponding second or third switching circuit by other quantities. For example, in another example, the first switching circuits 910-1 to 910-4 may be activated by control signals representing 0 degree, 90 degree, 180 degree, and 275 degree phase shifted versions of the LO signal; the second switching circuits 912-1 to 912-4 may be activated by control signals representing 185 degree, 275 degree, 5 degree, and 95 degree phase shifted versions of the LO signal; and the third switching circuits 914-1 to 914-4 may be activated by control signals representing 185 degree, 275 degree, 5 degree, and 95 degree offset versions of the LO signal, as shown in Table 4.

[0087] Table 4

[0088]

[0089] and Figure 8 The same as the converter 800, in Fig. 9 An amplifier 920, such as an LNA, may be added before the converter 900 to form the front-end circuitry of a wireless receiver. Specifically, the amplifier (e.g., LNA) 920 may be used to receive a single-ended RF signal captured by an antenna, generate a single-ended amplified version of the received signal and provide it to the input port 900 of the converter 902. The output V_OUT (V_OUT_P and V_OUT_N) of the converter 900 may then be provided to a mixer and / or baseband processing components.

[0090] Reference Fig.10 , which shows a single-ended LNA and a subsequent Fig. 9 The frequency response 1002 of the front-end circuit of the single-ended to differential signal converter 900 and the LNA and subsequent single-ended N-channel filter (e.g., Figure 5 1004 of the front-end circuit of the single-ended N-channel filter 500). In these examples, the center frequency of the N-channel filter is 2.0 GHz (i.e., the frequency of the LO signal used to control the switching unit of the N-channel filter is 2.0 GHz). Fig.10 It can be seen that using Fig. 9 The single-ended to differential signal converter 900 replaces the single-ended N-channel filter, so that the gain at the center frequency (2.0 GHz) is increased by 6 dB and the out-of-band suppression is significantly improved.

[0091] Accordingly, the single-ended to differential signal converters 800, 900 described herein can provide a set of symmetrical differential outputs from a single-ended input signal without consuming DC power, with minimal increase in implementation area, minimal complexity of the control circuit, and minimal impact on noise. In addition, in some cases (e.g., Fig. 9 ), gain enhancement and / or improved out-of-band rejection may be achieved for a corresponding single-ended output. When the converter is used in a wireless receiver, the improved out-of-band rejection may reduce the linearity requirements of stages and / or components after the converter.

[0092] Reference Fig.11 , which shows an example method 1100 for converting a single-ended signal to a differential signal pair. The method 1100 starts at blocks 1102, 1104, and 1106. At block 1102, an input signal is sequentially connected to each of a plurality of low-pass filter circuits (e.g., low-pass filter circuits 808-1 to 808-4 or 908-1 to 908-4). At block 1104, a first signal of a differential signal pair is generated by outputting the signals generated by the low-pass filter circuits in the same order via a first switching circuit associated with the low-pass filter circuit (e.g., switching circuits 810-1 to 810-4 or 914-1 to 914-4). At block 1106, a second signal of a differential signal pair is generated by outputting the signals generated by the low-pass filter circuits in the same order via a second switching circuit associated with the low-pass filter circuit (e.g., switching circuits 812-1 to 812-4 or 912-1 to 912-4). The first and second signals in the differential signal pair include signals generated by the same low pass filter circuit at phase offset periods.

[0093] In some cases, the input signal can be connected to multiple low pass filter circuits using a first switching circuit associated with the low pass filter circuit. In other cases, the input signal can be connected to multiple low pass filter circuits using a third switching circuit associated with the low pass filter circuit.

[0094] Applicants hereby disclose separately each individual feature described herein and any combination of two or more such features. With the common knowledge of those skilled in the art, such features or combinations can be implemented as a whole based on this specification, without considering whether such features or combinations of features can solve any problem disclosed herein; and without causing any impact on the scope of the claims. This application shows that various aspects of the present invention can be composed of any such individual features or combinations of features. In view of the foregoing description, it will be obvious to those skilled in the art that various modifications can be made within the scope of the present invention.

Claims

1. A single-ended to differential signal converter, characterized in that: include: Input port, used to receive single-ended signals; A first output port, used to output a first signal in a differential signal pair; A second output port, used to output the second signal in the differential signal pair; as well as An N-channel filter including a plurality of channels, each channel including a low-pass filter circuit, the low-pass filter circuit selectively connected to the input port, selectively connected to the first output port, and selectively connected to the second output port; Each channel also includes: a first switching circuit, which, when activated, connects the first output port to the low-pass filtering circuit; and a second switching circuit, which, when activated, connects the second output port to the low-pass filtering circuit; Each channel further comprises a third switching circuit, which, when activated, connects the input port to the low-pass filtering circuit.

2. The single-ended to differential signal converter according to claim 1, characterized in that: The first switching circuits of the plurality of channels are activated in sequence, and the third switching circuits of the plurality of channels are activated in the same sequence.

3. The single-ended to differential signal converter according to claim 2, characterized in that: The third switching circuit of one channel is activated by a third control signal having a different phase from the first and second control signals.

4. The single-ended to differential signal converter according to claim 3, characterized in that: The phase of the third control signal differs from the phase of one of the first and second control signals by 360 / n, where n is the number of channels in the N-channel filter.

5. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: The third switching circuit of one channel and the first or second switching circuit of another channel are activated by the same control signal.

6. The single-ended to differential signal converter according to claim 1, characterized in that: The input port is short-connected to the first output port so that when the first switch of a channel is activated, the input port and the first output port are connected to the low-pass filter circuit of the channel.

7. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: The first switching circuit of one channel and the second switching circuit of another channel are activated by the same control signal.

8. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: The first switching circuit of at least one channel comprises a single switch.

9. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: The second switching circuit of at least one channel includes a single switch.

10. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: When a low pass filter circuit is connected to the input port at the same frequency as the single ended signal, the low pass filter circuit receives a baseband version of the single ended signal which is converted by the low pass filter circuit to a filtered baseband signal.

11. The single-ended to differential signal converter according to claim 10, characterized in that: When a control signal having the same frequency as the single-ended signal activates the first switching circuit, the first switching circuit up-converts the filtered baseband signal to an original frequency band of the single-ended signal.

12. The single-ended to differential signal converter according to claim 11, characterized in that: When a control signal having the same frequency as the single-ended signal activates the second switching circuit, the second switching circuit up-converts the filtered baseband signal to an original frequency band of the single-ended signal.

13. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: The single-ended signal is a radio frequency signal.

14. The single-ended to differential signal converter according to claim 13, characterized in that: The first and second signals of the differential signal pair are radio frequency signals.

15. The single-ended to differential signal converter according to any one of claims 1 to 4, characterized in that: At least one low pass filter circuit includes a capacitor connected in parallel with a resistor.

16. A front-end signal processing circuit, characterized in that: include: An amplifier for outputting a single-ended signal; as well as The single-ended to differential signal converter according to any one of claims 1 to 4, wherein the input port of the single-ended to differential signal converter is coupled to the output port of the amplifier.

17. A method for converting a single-ended input signal into a differential signal pair, characterized in that: include: Connecting the single-ended input signal to a plurality of low-pass filter circuits in sequence; generating a first signal of the differential signal pair by sequentially outputting a signal generated by one of the plurality of low-pass filter circuits via a first switching circuit associated with the low-pass filter circuit; as well as generating a second signal of the differential signal pair by sequentially outputting a signal generated by one of the plurality of low-pass filter circuits via a second switching circuit associated with the low-pass filter circuit; wherein the single-ended input signal is connected to the plurality of low-pass filter circuits using a third switching circuit associated with the low-pass filter circuit; The first signal and the second signal in the differential signal pair include signals generated by the same low-pass filter circuit.

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