WO2016006464A1

WO2016006464A1 - Calibration circuit and receiver

Info

Publication number: WO2016006464A1
Application number: PCT/JP2015/068337
Authority: WO
Inventors: トァンタンタ; 明秀崔; 英徳大國; 雅則古田
Original assignee: 株式会社東芝
Priority date: 2014-07-09
Filing date: 2015-06-25
Publication date: 2016-01-14
Also published as: JP2017157877A

Abstract

According to an embodiment of the present invention, a calibration circuit comprises a first detector, a second detector, a comparison unit, and a control circuit. The first detector is connected to a first output terminal of a single-phase differential conversion circuit, and generates a first detection signal by detecting a first detector input signal. The second detector is connected to a second output terminal of the single-phase differential conversion circuit, and generates a second detection signal by detecting a second detector input signal. The comparison unit compares a voltage of the first detection signal and a voltage of the second detection signal, and generates a comparison result signal indicating the comparison result. The control circuit sets a control code to a plurality of different values, and searches for a desired control code by analyzing the correspondence between the set control code and the comparison result signal corresponding to the set control code.

Description

Calibration circuit and receiver

Embodiment relates to calibration of input impedance of a differential amplifier.

Conventional calibration techniques for amplifier input impedance can be broadly classified into two types. The first calibration technique is to measure, for example, the reflected power while changing the control code of the variable impedance element, and search for a control code that minimizes the reflected power. The second calibration technique is to measure the amplitude of the output signal of the amplifier while changing the control code of the variable impedance element, and search for the control code that maximizes the amplitude.

The first calibration technique requires an expensive network analyzer to measure the reflected power with high accuracy. Therefore, the first calibration technique is unsuitable for simultaneously calibrating a large number of amplifiers, so that the productivity is low. Furthermore, since the first calibration technique cannot be applied after the product is shipped, it cannot compensate for deterioration of the amplifier due to a change in usage environment and aging.

The accuracy of the second calibration technique depends on the voltage stability of the amplifier input signal. Therefore, in order to achieve high accuracy in the second calibration technique, an expensive measurement system is required. Furthermore, since the amplitude change of the output signal of the amplifier is small with respect to the change of the control code, a highly sensitive amplitude detection circuit is required according to the second calibration technique. A high-sensitivity amplitude detection circuit has a larger design load and is more susceptible to external influences (for example, influence of manufacturing process, temperature, voltage, etc.) than a low-sensitivity detection circuit. In addition, the amplitude of the output signal of the amplifier does not change monotonously with changes in the control code. Therefore, since the second calibration technique cannot use a high-speed search algorithm such as a binary search method, the time required for calibration is long.

Embodiment is aimed at efficiently calibrating the input impedance of a differential amplifier.

According to the embodiment, the calibration circuit includes a single-phase differential conversion circuit, a first detector, a second detector, a comparison unit, and a control circuit. The single-phase differential conversion circuit has an input terminal, a first output terminal, and a second output terminal, includes an impedance variable element whose impedance changes depending on the control code, and converts the single-phase input signal to a differential output signal And convert. The first detector is connected to the first output terminal of the single-phase differential conversion circuit, and generates a first detection signal by detecting the first detector input signal. The second detector is connected to the second output terminal of the single-phase differential conversion circuit, and generates a second detection signal by detecting the second detector input signal. The comparison unit compares the voltage of the first detection signal and the voltage of the second detection signal, and generates a comparison result signal indicating the comparison result. The control circuit searches for a desired control code by setting the control code to a plurality of different values and analyzing the correspondence relationship between the set control code and the corresponding comparison result signal.

1 is a block diagram illustrating a calibration circuit according to a first embodiment. FIG. 2 is a circuit diagram illustrating the single-phase differential conversion circuit of FIG. 1. The graph which illustrates the change of | S11 | and V2 / V3 with respect to the change of the control code. The graph which illustrates the change of | S11 | with respect to the change of V2 / V3. The graph which illustrates the change of (V2-V3) with respect to the change of a control code. The block diagram which illustrates the calibration circuit concerning a 2nd embodiment. The block diagram which illustrates the calibration circuit concerning a 3rd embodiment. The graph which illustrates the change of V32 / V33 with respect to the change of a control code. The block diagram which illustrates the receiver concerning a 5th embodiment. The block diagram which illustrates the calibration circuit concerning a 4th embodiment. The graph which illustrates the change of (V2-V3 + _VDO ) and (V3-V2 + _VDO ) with respect to the change of a control code. The graph which illustrates the change of the comparison result signal with respect to the change of a control code.

Hereinafter, embodiments will be described with reference to the drawings. Hereinafter, the same or similar elements as those already described are denoted by the same or similar reference numerals, and redundant description is basically omitted.

(First embodiment)
A specific example of the calibration circuit according to the first embodiment is shown in FIG. The calibration circuit 100 in FIG. 1 functions as a part of the wireless receiver. The calibration circuit 100 has an input terminal, a first output terminal, and a second output terminal. The input terminal of the calibration circuit 100 is connected to the antenna 20. The first output terminal and the second output terminal of the calibration circuit 100 are respectively connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 30 as a low noise amplifier (LNA). The calibration circuit 100 converts the single-phase input signal into a differential output signal and outputs the differential output signal to the differential amplifier 30. When the input impedance of the differential amplifier 30 is calibrated, the input terminal of the calibration circuit 100 is directly or indirectly connected to the external signal source 10. Specifically, the input terminal of the calibration circuit 100 may be disconnected from the antenna 20 and connected to the signal source 10, or the antenna 20 receives a radio signal radiated from the signal source 10 and calibrates the received radio signal. You may supply to the input terminal of the circuit 100. FIG. The calibration circuit 100 calibrates the input impedance of the differential amplifier 30 using the single-phase input signal supplied from the signal source 10.

The calibration circuit 100 includes a single-phase differential conversion circuit 110, a detector 120, a detector 130, a comparison unit 140, and a matching control circuit 150.

The single-phase differential conversion circuit 110 has an input terminal, a first output terminal, a second output terminal, and a control terminal. The input terminal of the single phase differential conversion circuit 110 is connected to the input terminal of the calibration circuit 100. The first output terminal of the single-phase differential conversion circuit 110 is commonly connected to the input terminal of the detector 120 and the first output terminal of the calibration circuit 100. The second output terminal of the single-phase differential conversion circuit 110 is commonly connected to the input terminal of the detector 130 and the second output terminal of the calibration circuit 100. The control terminal of the single phase differential conversion circuit 110 is connected to the output terminal of the matching control circuit 150.

The single-phase differential conversion circuit 110 includes an impedance variable element. The impedance of the variable impedance element changes depending on a control code input via the control terminal of the single-phase differential conversion circuit 110.

The single-phase differential conversion circuit 110 converts a single-phase input signal into a differential output signal. The differential output signal includes a first output signal output via the first output terminal and a second output signal output via the second output terminal.

The single-phase differential conversion circuit 110 may include an inductor 111, an inductor 112, an inductor 113, and a variable capacitor 114, for example, as shown in FIG.

The inductor 111 has a first terminal and a second terminal. The first terminal of the inductor 111 is connected in common to the input terminal of the single-phase differential conversion circuit 110 and the first terminal of the inductor 113. The second terminal of the inductor 111 is connected in common to the first output terminal of the single-phase differential conversion circuit 110 and the first terminal of the variable capacitor 114.

The inductor 112 has a first terminal and a second terminal. The first terminal of the inductor 112 is connected to the second terminal of the inductor 113. The second terminal of the inductor 112 is connected to the second output terminal of the single-phase differential conversion circuit 110 and the second terminal of the capacitor 114. The inductance of the inductor 112 is equal to the inductance of the inductor 111.

The inductor 113 has a first terminal and a second terminal. The first terminal of the inductor 113 is connected in common to the input terminal of the single-phase differential conversion circuit 110 and the first terminal of the inductor 111. The second terminal of the inductor 113 is connected to the first terminal of the inductor 112.

The variable capacitor 114 has a first terminal and a second terminal. The first terminal of the variable capacitor 114 is connected in common to the first output terminal of the single-phase differential conversion circuit 110 and the second terminal of the inductor 111. The second terminal of the variable capacitor 114 is connected in common to the second output terminal of the single-phase differential conversion circuit 110 and the second terminal of the inductor 112. The inductor 113 and the variable capacitor 114 act so that the first output signal and the second output signal of the single-phase differential conversion circuit 110 become differential signals.

The variable capacitor 114 corresponds to the aforementioned variable impedance element. That is, the capacitance of the variable capacitor 114 changes depending on the control code input via the control terminal of the single-phase differential conversion circuit 110.

Note that the variable capacitor 114 may be replaced with various variable impedance elements including a variable inductor. For example, the variable impedance element may be a plurality of inductors whose connections can be switched using a switch. Alternatively, the variable impedance element may include an inductor, a ferrite, and a mechanism that can change a relative positional relationship between the inductor and the ferrite.

The detector 120 has an input terminal and an output terminal. The input terminal of the detector 120 is commonly connected to the first output terminal of the single-phase differential conversion circuit 110 and the first output terminal of the calibration circuit 100. The output terminal of the detector 120 is connected to the first input terminal of the comparison unit 140. The detector 120 obtains the first detection signal by detecting the first output signal (first detector input signal) of the single-phase differential conversion circuit 110. The first detection signal indicates the amplitude of the first output signal.

The detector 130 has an input terminal and an output terminal. The input terminal of the detector 130 is connected in common to the second output terminal of the single-phase differential conversion circuit 110 and the second output terminal of the calibration circuit 100. The output terminal of the detector 130 is connected to the second input terminal of the comparison unit 140. The detector 130 detects the second output signal (second detector input signal) of the single-phase differential conversion circuit 110 to obtain a second detection signal. The second detection signal indicates the amplitude of the second output signal.

The comparison unit 140 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparison unit 140 is connected to the output terminal of the detector 120. The second input terminal of the comparison unit 140 is connected to the output terminal of the detector 130. The output terminal of the comparison unit 140 is connected to the input terminal of the matching control circuit 150. The comparison unit 140 receives the first detection signal and the second detection signal from the detector 120 and the detector 130, and compares these voltages. The comparison unit 140 outputs a comparison result signal indicating the comparison result to the matching control circuit 150. For example, if the voltage of the first detection signal is V2 and the voltage of the second detection signal is V3, the comparison result signal may indicate (V2-V3) itself or its sign, or V2 / V3 may be It may be indicated, (V3-V2) itself or its sign may be indicated, or V3 / V2 may be indicated.

The matching control circuit 150 has an input terminal and an output terminal. The input terminal of the matching control circuit 150 is connected to the output terminal of the comparison unit 140. The output terminal of the matching control circuit 150 is connected to the control terminal of the single-phase differential conversion circuit 110.

The matching control circuit 150 outputs a control code for controlling the impedance of the variable impedance element included in the single-phase differential conversion circuit 110 to the single-phase differential conversion circuit 110. More specifically, the matching control circuit 150 sets the control code to a plurality of different values when the input impedance of the differential amplifier 30 is calibrated. Then, the matching control circuit 150 receives a comparison result signal corresponding to the set control code from the comparison unit 140 and stores it in association with the control code. The matching control circuit 150 searches for an optimal (ie, desired) control code by analyzing a correspondence relationship between the stored control code and the comparison result signal. The optimum control code can be defined as a value that minimizes the reflected power at the input terminal of the single-phase differential conversion circuit 110, for example.

FIG. 3 exemplifies changes in | S11 | and V2 / V3 with respect to changes in the control code. Further, FIG. 4 illustrates the change in | S11 | with respect to the change in V2 / V3. Here, | S11 | represents the absolute value of the ratio of the reflected power to the incident power at the input terminal of the single-phase differential conversion circuit 110. The control code that minimizes | S11 | is the optimal control code. According to the examples of FIGS. 3 and 4, | S11 | is minimized when the control code = 19. Further, when the control code = 19, V2 / V3 is approximately 0 dB. Therefore, the matching control circuit 150 obtains an optimal control code by searching for a control code that satisfies V2≈V3.

As shown in FIG. 3, V2 / V3 (and V3 / V2) change monotonously with respect to the control code. Furthermore, as shown in FIG. 5, (V2-V3) (and (V3-V2)) also changes monotonously with respect to the control code. Therefore, the matching control circuit 150 can search for an optimal control code in a short time by using a high-speed search algorithm such as a binary search method.

Specifically, the matching control circuit 150 can search for an optimal control code as follows. First, the matching control circuit 150 sets the minimum control code (= C _min ) and the maximum control code (= C _max ), respectively, and accumulates the value or sign of (V2−V3) (step S1). .

Next, the matching control circuit 150 generates a code of (V2-V3) corresponding to the minimum control code (= C _min ) and a code of (V2-V3) corresponding to the maximum control code (= C _max ). Compare (step S2). If both signs are the same, V2> V3 or V2 <V3 is always established, so that the input impedance of the differential amplifier 30 cannot be calibrated. That is, an IC (Integrated Circuit) including the differential amplifier 30 is determined as a defective product, and the calibration process ends. On the other hand, if the two codes are not the same, the matching control circuit 150 substitutes C _min for the variable A and C _max for the variable B, and the process proceeds to step S3.

In step S3, the matching control circuit 150 determines whether A and B are adjacent integers (that is, | A−B | = 1). If A and B are adjacent integers, the process proceeds to step S8. Otherwise, the process proceeds to step S4.

In step S4, the matching control circuit 150 sets an integer C obtained by applying a floor function to the average value of the variables A and B as shown in the following formula (1) in the control code (V2− The value or sign of V3) is stored.

Next, the matching control circuit 150 determines the sign of (V2-V3) when the control code (= C) is set in step S4 (step S5). If the sign is the same as the sign when the control code (= A) is set, the matching control circuit 150 substitutes C for the variable A (step S6), and the process returns to step S3. On the other hand, if the sign is the same as the sign when the control code (= B) is set, the matching control circuit 150 substitutes C for the variable B (step S7), and the process returns to step S3.

In step S8, the matching control circuit 150 determines an optimal control code. Specifically, at the start of step S8, optimal control code candidate values are assigned to variable A and variable B, respectively. That is, one is the optimal control code and the other is the second most suitable control code. If the matching control circuit 150 cannot acquire the absolute value of (V2-V3), it is impossible to determine the superiority or inferiority of the two candidate values. Therefore, the matching control circuit 150 determines one of the two candidate values as an optimal control code. On the other hand, if the matching control circuit 150 can acquire the absolute value of (V2-V3), it is possible to determine the superiority or inferiority of the two candidate values. For example, the matching control circuit 150 may determine a candidate value that minimizes the absolute value of (V2-V3) as an optimal control code.

According to the above search processing, the matching control circuit 150 can search for an optimal control code in a short time. Specifically, assuming that the total number of values that can be set in the control code is N, the matching control circuit 150 sets the control code over the number of times I shown in the following formula (2). The optimal control code can be searched.

That is, even if N is doubled, the number of times that the matching control circuit 150 has to set a control code in order to search for an optimal control code is only increased by one. Therefore, the search process has a greater effect of reducing the search time as N increases. In general, the larger N is, the finer the input impedance of the differential amplifier 30 can be adjusted, so that the performance of the differential amplifier 30 can be further extracted. Specifically, even when the impedance matching frequency is a narrow band and the input impedance of the differential amplifier 30 needs to be calibrated over a wide band, an optimum control code is searched in a short time. be able to.

As described above, the calibration circuit according to the first embodiment calibrates the input impedance of the differential amplifier based on the differential output signal from the single-phase differential conversion circuit connected to the previous stage of the differential amplifier. If the input impedance is calibrated based on the differential amplification signal from the differential amplifier, a high power input signal cannot be used to avoid saturation of the differential amplification signal. On the other hand, since the calibration process of the input impedance is not affected by the saturation of the differential amplification signal, this calibration circuit can use a high-power input signal. That is, since the difference voltage between the two input signals of the comparison unit can be sufficiently increased, the input impedance can be accurately calibrated.

Also, since the calibration accuracy of the input impedance hardly depends on the absolute value of the output power in the external signal source, it is possible to meet the demand for the stability of the output power even if an inexpensive signal source is used. Furthermore, by dividing the signal generated by this signal source into a large number of signals with an inexpensive power distributor, the input impedances of a large number of differential amplifier circuits can be calibrated simultaneously.

Furthermore, since the voltage of the first output signal and the voltage of the second output signal of the single-phase differential conversion circuit are highly sensitive to the control code, the required accuracy of the detector and the comparator is low. Therefore, since this calibration circuit can be easily designed and manufactured, the manufacturing yield is high. Specifically, as shown in FIG. 5, when the level of a single-phase input signal supplied from an external signal source is −10 dBm, it corresponds to the optimal control code (= 19) (V2−V3). ) Is −0.6 mV, and (V2−V3) corresponding to the second most suitable control code (= 20) is 29.7 mV. Therefore, the error of the detector and the comparison unit is acceptable up to 30.3 mV.

(Second Embodiment)
A specific example of the calibration circuit according to the second embodiment is shown in FIG. The calibration circuit 200 in FIG. 6 functions as a part of the wireless receiver. The calibration circuit 200 has an input terminal, a first output terminal, and a second output terminal. The input terminal of the calibration circuit 200 is connected to the antenna 20. The first output terminal and the second output terminal of the calibration circuit 200 are respectively connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 30 as the LNA. The calibration circuit 200 converts the single-phase input signal into a differential output signal and outputs the differential output signal to the differential amplifier 30. When the input impedance of the differential amplifier 30 is calibrated, the input terminal of the calibration circuit 200 is directly or indirectly connected to the external signal source 10. Specifically, the input terminal of the calibration circuit 200 may be disconnected from the antenna 20 and connected to the signal source 10, or the antenna 20 receives a radio signal radiated from the signal source 10 and calibrates the received radio signal. You may supply to the input terminal of the circuit 200. FIG. The calibration circuit 200 calibrates the input impedance of the differential amplifier 30 using the single-phase input signal supplied from the signal source 10.

The calibration circuit 200 includes a single-phase differential conversion circuit 110, a detector 120, a detector 130, a comparison unit 140, a matching control circuit 150, a single-phase amplifier 260, and a single-phase amplifier 270. The comparison unit 140 and the matching control circuit 150 may be the same as or similar to the comparison unit 140 and the matching control circuit 150 of FIG.

The single-phase differential conversion circuit 110 has a first output terminal connected to the input terminal of the single-phase amplifier 260 instead of the input terminal of the detector 120 and the first output terminal of the calibration circuit 100, and the second 1 is different from the single-phase differential conversion circuit 110 in FIG. 1 in that the output terminal is connected to the input terminal of the single-phase amplifier 270 instead of the input terminal of the detector 130 and the second output terminal of the calibration circuit 100.

The detector 120 has the input terminal connected to the output terminal of the single-phase amplifier 260 instead of the first output terminal of the single-phase differential conversion circuit 110 and the first output terminal of the calibration circuit 100, as shown in FIG. Different from the vessel 120.

The detector 130 has the input terminal connected to the output terminal of the single-phase amplifier 270 instead of the second output terminal of the single-phase differential conversion circuit 110 and the second output terminal of the calibration circuit 100, as shown in FIG. Different from the vessel 130.

The single phase amplifier 260 has an input terminal and an output terminal. The input terminal of the single phase amplifier 260 is connected to the first output terminal of the single phase differential conversion circuit 110. The output terminal of the single phase amplifier 260 is commonly connected to the input terminal of the detector 120 and the first output terminal of the calibration circuit 200. By inserting the single-phase amplifier 260 between the single-phase differential conversion circuit 110 and the detector 120, the parasitic component of the detector 120 can be disconnected from the first output terminal of the single-phase differential conversion circuit 110.

The single-phase amplifier 260 receives the first output signal from the single-phase differential conversion circuit 110 and amplifies it to obtain a first amplified signal. Single phase amplifier 260 outputs the first amplified signal to detector 120.

Single phase amplifier 270 has an input terminal and an output terminal. The input terminal of the single phase amplifier 270 is connected to the second output terminal of the single phase differential conversion circuit 110. The output terminal of the single phase amplifier 270 is connected in common to the input terminal of the detector 130 and the second output terminal of the calibration circuit 200. By inserting the single-phase amplifier 270 between the single-phase differential conversion circuit 110 and the detector 130, the parasitic component of the detector 130 can be disconnected from the second output terminal of the single-phase differential conversion circuit 110. Single-phase amplifier 270 has the same characteristics as single-phase amplifier 260.

The single-phase amplifier 270 receives the second output signal from the single-phase differential conversion circuit 110 and amplifies it to obtain a second amplified signal. Single phase amplifier 270 outputs the second amplified signal to detector 130.

As described above, the calibration circuit according to the second embodiment inserts a single-phase amplifier between each output terminal of the single-phase differential conversion circuit and each detector. Therefore, according to this calibration circuit, the parasitic component of each detector can be separated from each output terminal of the single-phase differential conversion circuit, and the input impedance of the differential amplifier connected to the subsequent stage of the calibration circuit can be accurately calibrated. it can.

(Third embodiment)
A specific example of the calibration circuit according to the third embodiment is shown in FIG. The calibration circuit 300 in FIG. 7 functions as a part of the wireless receiver. The calibration circuit 300 has an input terminal, a first output terminal, and a second output terminal. The input terminal of the calibration circuit 300 is connected to the antenna 20. The first output terminal and the second output terminal of the calibration circuit 300 are respectively connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 30 as the LNA. The calibration circuit 300 converts the single-phase input signal into a differential output signal and outputs the differential output signal to the differential amplifier 30. When the input impedance of the differential amplifier 30 is calibrated, the calibration circuit 300 drives an internal current signal source as will be described later. The calibration circuit 300 calibrates the input impedance of the differential amplifier 30 using the current signal supplied from the current signal source. Note that the antenna 20 may be connected to the input terminal of the calibration circuit 300 or disconnected at the time of calibration.

The calibration circuit 300 includes a single-phase differential conversion circuit 110, a detector 120, a detector 130, a comparison unit 140, a matching control circuit 150, and a current signal source 380. The detector 130, the comparison unit 140, and the matching control circuit 150 may be the same as or similar to the detector 130, the comparison unit 140, and the matching control circuit 150 of FIG.

The single-phase differential conversion circuit 110 is different from the single-phase differential conversion circuit 110 of FIG. 1 in that the first output terminal is further connected to the output terminal of the current signal source 380. The detector 120 is different from the detector 120 of FIG. 1 in that the input terminal is further connected to the output terminal of the current signal source 380.

The current signal source 380 has an output terminal. The output terminal of the current signal source 380 is commonly connected to the first output terminal of the single-phase differential conversion circuit 110, the input terminal of the detector 120, and the first output terminal of the calibration circuit 300. The current signal source 380 is driven when the input impedance of the differential amplifier 30 is calibrated to generate a current signal. The current signal source 380 injects a current signal into the first output terminal of the single-phase differential conversion circuit 110.

The current signal source 380 includes an oscillator 381 and a voltage / current converter 382. The oscillator 381 is driven when the input impedance of the differential amplifier 30 is calibrated and generates an oscillation signal. The oscillator 381 outputs an oscillation signal to the voltage / current converter 382. The voltage / current converter 382 obtains the current signal by performing voltage / current conversion on the oscillation signal.

When the current signal is injected into the first output terminal of the single-phase differential conversion circuit 110, the single-phase differential conversion circuit 110 outputs the first output signal described above via the first output terminal. The second output signal described above is output through the two output terminals. Then, the detector 120 and the detector 130 obtain a first detection signal and a second detection signal, respectively. When the voltage of the first detection signal and the voltage of the second detection signal at the time of current signal injection are V32 and V33, respectively, V32 / V33 is V2 // in the first embodiment as illustrated in FIG. Behaves similarly to V3. Therefore, as described in the first embodiment, the matching control circuit 150 can search for an optimal control code (= 19) based on the first detection signal and the second detection signal.

The graph of FIG. 8 is drawn by measuring V32 and V33 with the input terminal of the single-phase differential conversion circuit 110 opened (that is, the antenna 20 is disconnected from the input terminal of the calibration circuit 100). ing. In this state, the condition of V32 = V33 is almost the same as the condition of V2 = V3.

On the other hand, in the state where the antenna 20 is connected, a certain amount of power is radiated from the antenna 20 by the injection of the current signal, so the condition of V32 = V33 is offset compared to the condition of V2 = V3. This offset amount depends on the characteristics of the antenna 20, but can be estimated by comparing the calibration result using the external signal source 10 and the calibration result using the current signal source 380 once, for example. Thereafter, it is possible to calibrate with high accuracy using the current signal source 380 by compensating for the estimated offset amount.

As described above, the calibration circuit according to the third embodiment includes the current signal source therein. Therefore, according to the calibration circuit, the input impedance of the differential amplifier connected to the subsequent stage of the calibration circuit can be calibrated using the current signal source. That is, since the deterioration of the differential amplifier due to changes in the usage environment and aging can be compensated for, it can be expected that the usage environment of the differential amplifier will be expanded and the life thereof extended.

7 corresponds to a configuration in which a current signal source 380 is added to the calibration circuit 100 in FIG. However, the calibration circuit according to the present embodiment may correspond to a configuration in which the current signal source 380 is added to the calibration circuit 200 of FIG. In this case, the output terminal of the current signal source 380 may be connected to the preceding stage rather than the subsequent stage of the single-phase amplifier 260.

(Fourth embodiment)
A specific example of the calibration circuit according to the fourth embodiment is shown in FIG. The calibration circuit 500 in FIG. 10 functions as a part of the wireless receiver. The calibration circuit 500 has an input terminal, a first output terminal, and a second output terminal. The input terminal of the calibration circuit 500 is connected to the antenna 20. The first output terminal and the second output terminal of the calibration circuit 500 are respectively connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 30 as the LNA. The calibration circuit 500 converts the single-phase input signal into a differential output signal and outputs the differential output signal to the differential amplifier 30. When the input impedance of the differential amplifier 30 is calibrated, the input terminal of the calibration circuit 500 is directly or indirectly connected to the external signal source 10. Specifically, the input terminal of the calibration circuit 400 may be disconnected from the antenna 20 and connected to the signal source 10, or the antenna 20 receives a radio signal radiated from the signal source 10 and calibrates the received radio signal. You may supply to the input terminal of the circuit 400. FIG. The calibration circuit 500 calibrates the input impedance of the differential amplifier 30 using the single-phase input signal supplied from the signal source 10.

Calibration circuit 500 includes a single-phase differential conversion circuit 110, a detector 120, a detector 130, a comparison unit 540, a matching control circuit 550, and a switching circuit 590.

The detector 120 is different from the detector 120 of FIG. 1 in that the output terminal is connected to the first input terminal of the switching circuit 590 instead of the first input terminal of the comparison unit 140. The detector 130 is different from the detector 130 of FIG. 1 in that the output terminal is connected to the second input terminal of the switching circuit 590 instead of the second input terminal of the comparison unit 140.

The switching circuit 590 has a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The first input terminal of the switching circuit 590 is connected to the output terminal of the detector 120. The second input terminal of the switching circuit 590 is connected to the output terminal of the detector 130. The first output terminal of the switching circuit 590 is connected to the first input terminal of the comparison unit 540. The second output terminal of the switching circuit 590 is connected to the second input terminal of the comparison unit 540.

The switching circuit 590 has a first operation state and a second operation state. The switching circuit 590 short-circuits between the first input terminal and the first output terminal during the first period in the first operation state, and between the second input terminal and the second output terminal. Short circuit. On the other hand, the switching circuit 590 short-circuits between the first input terminal and the second output terminal in the second period in the second operation state, and the second input terminal and the first output terminal Short-circuit between the two.

The comparison unit 540 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparison unit 540 is connected to the first output terminal of the switching circuit 590. The second input terminal of the comparison unit 540 is connected to the second output terminal of the switching circuit 590. The output terminal of the comparison unit 540 is connected to the input terminal of the matching control circuit 550.

The comparison unit 540 compares the first voltage (V _inp ) applied to the first input terminal and the second voltage (V _inm ) applied to the second input terminal. Comparison unit 540 outputs a comparison result signal indicating the comparison result to matching control circuit 550. However, the comparison unit 540 has a DC offset (V _DO ). As this DC offset (V _DO ), a basic DC offset depending on the basic circuit configuration of the comparison unit 540 may be used as it is. If the basic DC offset is not an appropriate magnitude, this is intentionally used. You may adjust.

Specifically, the comparison unit 540 generates a comparison result signal (V _out ) represented by the following mathematical formula (3).

In Equation (3), Sgn (•) is a sign function and returns the sign of •. That is, in the first period in which the switching circuit 590 is in the first operation state, the comparison result signal indicates the sign of (V2−V3 + V _DO ). On the other hand, in the second period in which the switching circuit 590 is in the second operation state, the comparison result signal indicates the sign of (V3−V2 + V _DO ).

Matching control circuit 550 has an input terminal and an output terminal. The input terminal of the matching control circuit 550 is connected to the output terminal of the comparison unit 140. The output terminal of the matching control circuit 550 is connected to the control terminal of the single-phase differential conversion circuit 110.

Matching control circuit 550 outputs a control code for controlling the impedance of the variable impedance element included in single-phase differential conversion circuit 110 to single-phase differential conversion circuit 110. More specifically, when the input impedance of the differential amplifier 30 is calibrated, the matching control circuit 550 includes a first period in which the switching circuit 590 is in the first operation state and a second period in which the switching circuit 590 is in the second operation state. Each of the control codes is set to a plurality of different values. Then, the matching control circuit 550 receives a comparison result signal corresponding to the set control code from the comparison unit 540 and stores it in association with the control code. The matching control circuit 550 searches for an optimal control code by analyzing the correspondence between the stored control code and the comparison result signal. The optimum control code is, for example, a value that minimizes the absolute value of the difference between the voltage of the first detection signal and the voltage of the second detection signal.

FIG. 11 illustrates changes in (V2−V3 + V _DO ) and (V3−V2 + V _DO ) with respect to changes in the control code. In the example of FIG. 11, V _DO = 50 mV is set. According to FIG. 11, when the control code = 19, (V2−V3 + V _DO ) ≈V _DO and (V3−V2 + V _DO ) ≈V _DO , that is, V2≈V3. Therefore, the optimal control code = 19.

However, the comparison result signal indicates these codes, not (V2−V3 + V _DO ) or (V3−V2 + V _DO ) itself. That is, when (V2−V3 + V _DO ) and (V3−V2 + V _DO ) change as shown in FIG. 11, the comparison result signal changes as illustrated in FIG. As shown in FIG. 12, the sign of (V2−V3 + V _DO ) and the sign of (V3−V2 + V _DO ) are different for most control codes, but the control codes around the optimum control code (= 19). In contrast, the sign of (V2−V3 + V _DO ) and the sign of (V3−V2 + V _DO ) match.

Therefore, the matching control circuit 550 includes one or more matching result signals obtained in the first period in which the switching circuit 590 is in the first operation state and the second period in which the switching circuit 590 is in the second operation state. A control code (“18”, “19”, “20” in the example of FIG. 12) is extracted. Then, the matching control circuit 550 determines the median value (“19” in the example of FIG. 12) in the extracted control code as the optimal control code. In the vicinity of the optimum control code, since (V2-V3) and (V3-V2) change substantially linearly with respect to the change of the control code, the total number of extracted control codes is usually an odd number. However, an even number of control codes may be extracted due to the influence of noise or the like. When an even number of control codes are extracted, matching control circuit 550 may determine a value obtained by applying a floor function or a ceiling function to the median value of the extracted control codes as a control code. .

As described above, the calibration circuit according to the fourth embodiment includes a first period in which two detection signals are input as they are to a comparison unit having a DC offset and a second period in which these detection signals are interchanged. The change of the comparison result signal is analyzed over each. Then, the calibration circuit determines an optimal control code from the control codes in which the signs indicated by the comparison result signals match in the first period and the second period. Therefore, according to this calibration circuit, an optimum control code can be searched with high accuracy regardless of the basic DC offset depending on the basic circuit configuration of the comparison unit. Furthermore, according to this calibration circuit, the comparison unit is not required to have the ability to detect the absolute value of the difference voltage between the two input signals.

(Fifth embodiment)
The receiver according to the fifth embodiment includes the calibration circuit according to any of the first to fourth embodiments described above, and can configure the input impedance of the differential amplifier as the LNA. Specifically, the receiver according to the present embodiment includes an antenna 20, a calibration circuit 400, a differential amplifier 30, and a demodulator 40, as illustrated in FIG.

The antenna 20 receives an RF signal transmitted by a transmission device (not shown). The antenna 20 outputs an RF signal to the calibration circuit 400.

The calibration circuit 400 obtains a differential output signal from the RF signal as a single-phase input signal. The calibration circuit 400 supplies the differential output signal to the differential amplifier 30. The calibration circuit 400 corresponds to the calibration circuit according to any of the first to fourth embodiments described above. That is, when the input impedance of the differential amplifier 30 is calibrated, the calibration circuit 400 searches for an optimal control code for the variable impedance element not shown in FIG.

The differential amplifier 30 inputs a differential output signal from the calibration circuit 400. The differential amplifier 30 obtains a differential amplified signal by amplifying the differential output signal. The differential amplifier 30 outputs the differential amplified signal to the demodulator 40.

The demodulator 40 obtains received data by down-converting and demodulating the differential amplified signal.

As described above, the receiver according to the fifth embodiment includes the calibration circuit according to any of the first to fourth embodiments described above. Therefore, according to this receiver, the input impedance of the differential amplifier as the LNA can be calibrated efficiently.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

Claims

Single-phase differential conversion that has an input terminal, a first output terminal, and a second output terminal, includes an impedance variable element whose impedance changes depending on the control code, and converts a single-phase input signal into a differential output signal Circuit,
A first detector connected to a first output terminal of the single-phase differential conversion circuit and generating a first detection signal by detecting a first detector input signal;
A second detector connected to a second output terminal of the single-phase differential conversion circuit and generating a second detection signal by detecting a second detector input signal;
A comparison unit that compares the voltage of the first detection signal and the voltage of the second detection signal and generates a comparison result signal indicating a comparison result;
A calibration circuit comprising: a control circuit for searching for a desired control code by setting the control code to a plurality of different values and analyzing a correspondence relationship between the set control code and a comparison result signal corresponding thereto.
The control circuit determines, as the desired control code, a control code that is set when an absolute value of a voltage difference between the voltage of the first detection signal and the voltage of the second detection signal is minimum. Item 1. Calibration circuit.
The calibration circuit according to claim 1, wherein the control circuit searches for the desired control code by performing a binary search.
A first single-phase amplifier inserted between a first output terminal of the single-phase differential conversion circuit and the first detector;
The calibration circuit according to claim 1, further comprising: a second single-phase amplifier inserted between the second output terminal of the single-phase differential conversion circuit and the second detector.
2. The calibration circuit according to claim 1, further comprising a current signal source that generates a current signal and injects the current signal into the first output terminal of the single-phase differential conversion circuit.
The comparison result signal indicates a sign of a voltage obtained by subtracting the voltage of the second detection signal from the voltage of the first detection signal and adding a DC offset in the first period, The second period different from the period of 1 indicates a sign of a voltage obtained by subtracting the voltage of the first detection signal from the voltage of the second detection signal and adding the DC offset. Item 1. Calibration circuit.
The control circuit extracts at least one control code in which the comparison result signal in the first period matches the comparison result signal in the second period, and a median value of the extracted at least one control code 7. The calibration circuit of claim 6, wherein the desired control code is determined based on:
A calibration circuit according to claim 1;
A differential amplifier that obtains a differential amplified signal by amplifying the differential output signal;
A demodulator that obtains received data by down-converting and demodulating the differential amplified signal.