Low-phase-shift numerical control attenuator

Abstract

The utility model belongs to the technical field of numerical control attenuators, and discloses a low-phase-shift numerical control attenuator which comprises a first attenuation bit unit, a second attenuation bit unit, a third attenuation bit unit, a fourth attenuation bit unit, a fifth attenuation bit unit and a sixth attenuation bit unit which are arranged in a cascade mode. The attenuation bits of the first attenuation bit unit, the second attenuation bit unit, the third attenuation bit unit, the fourth attenuation bit unit, the fifth attenuation bit unit and the sixth attenuation bit unit are 8dB, 1dB, 0.5 dB, 2dB, 4dB and 16dB respectively, the second attenuation bit unit and the third attenuation bit unit are of a deformed T-shaped structure, and the fourth attenuation bit unit and the fifth attenuation bit unit are of a pi-shaped attenuation network structure. The sixth attenuation bit unit is of a switch path attenuator structure, and the first attenuation bit unit comprises two fifth attenuation bit units which are connected in series. The low-phase-shift numerical control attenuator has the characteristics of low insertion loss, low additional phase shift, high attenuation precision, high linearity and the like.

Description

Technical Field

[0001] The utility model belongs to the technical field of digital controlled attenuators, and in particular relates to a low phase shift digital controlled attenuator. Background Art

[0002] Many electronic devices (such as radar, communication, radio LAN, GPS, etc.) need to quantitatively attenuate high-frequency and medium-frequency signals. This attenuation is essentially a process of accurately quantifying high-frequency and medium-frequency signals. The accuracy will directly affect the performance indicators of these devices or the test of their performance indicators, and thus affect their performance. Therefore, it is necessary to seek an attenuator with small size, high accuracy, wide bandwidth, fast switching speed and easy use.

[0003] Switch-type digital attenuator: The reference path of the switch-type digital attenuator is generally realized by a transmission line with low loss. When the signal does not need to be attenuated, the signal flows from the input end of the circuit through the reference path and then flows out from the output port. At this time, the working state of the attenuator is the reference state, and the circuit only produces a small amount of insertion loss. The attenuation path of the switch-type attenuator is generally realized by a resistor network. The signal flows through the attenuation path, and the signal power is absorbed by the resistor network and converted into heat to achieve the attenuation function of the signal. A large number of single-pole double-throw switches are required in the circuit structure of the switch-type digital attenuator, so the attenuator performance is highly dependent on the switch performance. Two single-pole double-throw switches are required to connect each attenuation unit, and a large number of single-pole double-throw switches will also significantly increase the insertion loss of the attenuator. As the number of switches increases, the size of the attenuator chip and T / R components increases, and the manufacturing cost also increases. Therefore, the switch-type digital attenuator has not been widely adopted by the industry.

[0004] Distributed CNC attenuator: In actual circuit design, transistor switches and resistors of different resistance values ​​are usually used to replace variable resistors to achieve different degrees of attenuation; adjacent variable resistors are often connected by quarter-wavelength transmission lines to achieve input and output impedance matching. Each resistor is assigned a transistor switch. When the switch is turned on, a signal path to the ground is generated, resulting in a certain amount of attenuation, thereby realizing multi-bit CNC functions; by changing the resistance value of the resistor, each branch signal is controlled to achieve different degrees of attenuation, thereby achieving high-precision attenuation control. Because the circuit is in the reference state, that is, when all the switches in the parallel branch are in the disconnected state, the input and output ports are completely connected by several transmission lines. The signal will pass directly from the transmission line without passing through any transistor switch, so it is not affected by the parasitic effects of the transistor device, and the signal is almost not attenuated. Therefore, the distributed CNC attenuator has extremely small insertion loss characteristics and wide bandwidth characteristics. A large number of transmission lines are used in the distributed CNC attenuator structure, so the overall size of the attenuator chip will be relatively large, which is also not in line with the development trend of circuit miniaturization. Utility Model Content

[0005] The utility model aims to solve the above technical problems at least to a certain extent. To this end, the utility model aims to provide a low phase shift digital controlled attenuator.

[0006] The technical solution adopted by the utility model is:

[0007] A low phase shift digitally controlled attenuator comprises a first attenuation bit unit, a second attenuation bit unit, a third attenuation bit unit, a fourth attenuation bit unit, a fifth attenuation bit unit and a sixth attenuation bit unit which are arranged in cascade; the attenuation bits of the first attenuation bit unit, the second attenuation bit unit, the third attenuation bit unit, the fourth attenuation bit unit, the fifth attenuation bit unit and the sixth attenuation bit unit are 8dB, 1dB, 0.5dB, 2dB, 4dB and 16dB respectively; the second attenuation bit unit and the third attenuation bit unit are deformed T-type structures, the fourth attenuation bit unit and the fifth attenuation bit unit are π-type attenuation network structures, the sixth attenuation bit unit is a switch path attenuator structure, and the first attenuation bit unit comprises two fifth attenuation bit units connected in series.

[0008] Preferably, the switch path attenuator structure comprises:

[0009] A single-pole double-throw switch is used to realize the selection of the reference path and the attenuation path; there are two single-pole double-throw switches;

[0010] A resistor attenuation network is used to achieve signal attenuation in an attenuation state;

[0011] Transmission line used to compensate for the phase difference between a reference path and an attenuated path.

[0012] The beneficial effects of the utility model are:

[0013] The utility model provides a low phase shift digital controlled attenuator, including six attenuation bit units, with a large attenuation span, low insertion loss, low additional phase shift, high attenuation accuracy and high linearity. The built-in logic control circuit can effectively reduce the control signal wiring area, reduce the size of the GaAs attenuator chip and T / R components, thereby reducing the manufacturing cost; the use of positive voltage power supply makes the circuit more convenient and easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a circuit structure diagram of the low phase shift digital controlled attenuator of the utility model.

[0015] Figure 2 It is a schematic diagram of a deformed T-shaped structure of the utility model.

[0016] Figure 3 It is a schematic diagram of the π-type attenuation network structure of the utility model.

[0017] Figure 4 It is a schematic diagram of the switch path attenuator structure of the utility model.

[0018] Figure 5 It is an equivalent circuit diagram of the π-type attenuation network structure of the utility model in a reference state.

[0019] Figure 6 It is an equivalent circuit diagram of the π-type attenuation network structure of the utility model in the attenuation state.

[0020] Figure 7 The utility model discloses a low phase shift digital controlled attenuator. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the utility model to clearly and completely describe the technical solution of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, but not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0022] It should be understood that it should also be noted that in the embodiment, the functions / actions that appear may be different from the order in which the drawings appear. For example, depending on the functions / actions involved, they can actually be executed substantially concurrently, or two figures shown in succession can sometimes be executed in the reverse order.

[0023] like Figures 1 to 7 As shown, a low phase shift digital controlled attenuator of this embodiment is formed by cascading 6 attenuation units with different attenuation positions. Each basic attenuation unit is controlled by an independent complementary digital level. The switching between the reference state and the attenuation state is realized by controlling the series switch tube and the parallel switch tube. The cascade order of the attenuation position is adjusted according to the linearity, load effect and power handling capacity of the attenuator. There are 64 cascade orders for the 6 attenuation units. Different cascade modes have a greater impact on the overall circuit. In order to reduce the impact of the impedance mismatch between the attenuation levels on the performance, firstly, two attenuation units are cascaded, and a microstrip line of appropriate length is connected between the attenuation units to absorb the influence of parasitic capacitance. When adding the next attenuation unit, a sequence with the least impact on the overall performance should be selected. When cascading, the attenuation units with good port standing wave performance are placed at both ends to optimize the overall performance. According to the port characteristics of each attenuation unit, the attenuation units of the low phase shift digital controlled attenuator are arranged in 8dB, 1dB, 0.5dB, 2dB, 4dB, and 16dB, which can achieve better amplitude and phase characteristics.

[0024] Specifically, the low phase-shift digitally controlled attenuator includes a first attenuation bit unit, a second attenuation bit unit, a third attenuation bit unit, a fourth attenuation bit unit, a fifth attenuation bit unit, and a sixth attenuation bit unit arranged in cascade; the attenuation bits of the first attenuation bit unit, the second attenuation bit unit, the third attenuation bit unit, the fourth attenuation bit unit, the fifth attenuation bit unit, and the sixth attenuation bit unit are 8dB, 1dB, 0.5dB, 2dB, 4dB, and 16dB, respectively.

[0025] like Figure 2 As shown, the second attenuation bit unit and the third attenuation bit unit are deformed T-type structures. The deformed T-type structure has fewer active devices, higher attenuation accuracy and lower insertion loss, but the attenuation amplitude range is small, which is more suitable for attenuation units with smaller attenuation amplitudes. The switch tube is connected in series with the resistor to the ground. The switch tube uses two 2*25 size tubes in series, which can greatly reduce the off capacitance of the switch tube in the off state to achieve better phase characteristics. At the same time, adding a transmission line of a specific length at the input and output ends can ensure excellent input and output standing wave coefficients. When the control voltage Vctl1 is low, SW1 is cut off and the attenuation bit works in the on state; when the control voltage Vctl1 is high, SW1 is turned on and the attenuation bit works in the attenuation state. The attenuation is mainly changed by adjusting the grounding resistance.

[0026] like Figure 3 As shown, the fourth attenuation bit unit and the fifth attenuation bit unit are π-type attenuation network structures. The π-type attenuation network structure is realized by adding a switch tube to the π-type resistor network to control the on and off. It has two signal paths to the ground and is suitable for the design of medium and large attenuation bits. When the control voltage Vctl1 is high and Vctl2 is low, SW1 is turned on and SW2 is turned off, and the attenuation bit works in the on state; when the control voltage Vctl2 is low and Vctl1 is high, SW1 is turned off and SW2 is turned on, and the attenuation bit works in the attenuation state.

[0027] The first attenuation bit unit includes two fifth attenuation bit units connected in series.

[0028] like Figure 4 As shown, the sixth attenuation bit unit is a switch path attenuator structure, which includes two single-pole double-throw switches, a resistor attenuation network and a transmission line. The single-pole double-throw switch is used to realize the selection of the reference path and the attenuation path; the resistor attenuation network is used to realize the signal attenuation in the attenuation state; and the transmission line is used to compensate for the phase difference between the reference path and the attenuation path.

[0029] Due to the parasitic parameters of the switch tube, resistor, and capacitor in the circuit, each attenuation position has an additional phase shift in the attenuation state compared to the conduction state. In order to minimize the additional phase shift, this embodiment uses capacitor compensation technology. In the small attenuation position, fewer components are used and a structure with multiple small-sized switch tubes connected in parallel to the ground is adopted. The additional phase shift is very small and no phase compensation is required. The remaining attenuation positions need to introduce capacitor compensation because of their more complex structures. Figure 5 The equivalent circuit diagram of the π-type attenuation network structure in the reference state is given. In the reference state, SW1 is represented by the on-resistance Ron1, and SW2 and SW3 are represented by the off-capacitance Coff2 and Coff3. Because the resistance of R1 is much larger than the on-resistance of the switch tube, the signal is basically transmitted from the equivalent on-resistance of the switch tube with low transmission impedance. At this time, the signal loss consumed in the equivalent resistance is represented by the insertion loss of the attenuation bit. The two paths connected in series from the off-capacitance and the attenuation resistance to the ground can be regarded as a low-pass path, which will cause the output signal phase to lag behind the input signal phase. Figure 6 The equivalent circuit diagram of the π-type attenuation network structure in the attenuation state is given.

[0030] In the attenuation state, SW1 behaves as a turn-off capacitor Coff1, and SW2 and SW3 behave as on-resistances Ron2 and Ron3. Because the transmission reactance value of Coff1 is much larger than the attenuation network reactance value composed of the equivalent resistance of the switch tube and the attenuation resistance, the signal is basically transmitted from the resistance attenuation. At this time, the signal loss consumed in the resistance attenuation network is manifested as the attenuation amount of the attenuation position. The turn-off capacitance of the switch tube can be regarded as a high-pass path at this time, which will cause the output signal phase to be ahead of the input signal phase. In order to achieve low additional phase shift in the attenuation state, capacitor compensation needs to be added. By connecting the compensation capacitor Cp in parallel to R2 and R3 to form an equivalent low-pass filter structure, phase compensation can be effectively achieved. By selecting a suitable capacitance value, low additional phase shift can be achieved without basically affecting the attenuation value of the attenuation unit. The structure of the large attenuation position is more complicated. Compared with the π-type attenuation network structure, two single-pole double-throw switches are added. The additional phase shift caused by parasitic parameters is larger. Therefore, when connecting the compensation capacitor in parallel to the ground resistors R2 and R3, it is necessary to add a microstrip line of appropriate length at both ends of the R1 resistor for compensation.

[0031] like Figure 7The figure shows the layout simulation of the low phase shift digital controlled attenuator. The low phase shift digital controlled attenuator is designed based on GaAs0.25μm pHEMT process. The chip works with -5V power supply, TTL control mode, and the control voltage is 0 / 5V. The step is 0.5dB, and the maximum attenuation is 31.5dB. In the frequency range of (DC~18)GHz, the insertion loss is <4.5dB, the accuracy of all attenuation states meets ±(0.2+4%ATT), the additional phase shift is <±2°, the input standing wave coefficient is <1.5, and the output standing wave coefficient is <1.5. The chip area is 2.4*1.2*0.1(μm3).

[0032] The present utility model is not limited to the above-mentioned optional implementation modes. Anyone can derive other various forms of products under the inspiration of the present utility model. However, no matter what changes are made in the shape or structure, all technical solutions that fall within the scope defined by the claims of the present utility model fall within the protection scope of the present utility model.

Claims

1. A low phase shift digitally controlled attenuator, characterized in that: It includes a first attenuation bit unit, a second attenuation bit unit, a third attenuation bit unit, a fourth attenuation bit unit, a fifth attenuation bit unit and a sixth attenuation bit unit which are arranged in cascade; the attenuation bits of the first attenuation bit unit, the second attenuation bit unit, the third attenuation bit unit, the fourth attenuation bit unit, the fifth attenuation bit unit and the sixth attenuation bit unit are 8dB, 1dB, 0.5dB, 2dB, 4dB and 16dB respectively; the second attenuation bit unit and the third attenuation bit unit are deformed T-type structures; the fourth attenuation bit unit and the fifth attenuation bit unit are π-type attenuation network structures; the sixth attenuation bit unit is a switch path attenuator structure; the first attenuation bit unit includes two fifth attenuation bit units connected in series.

2. The low phase shift digitally controlled attenuator according to claim 1, characterized in that: The switch path attenuator structure comprises: A single-pole double-throw switch is used to realize the selection of the reference path and the attenuation path; there are two single-pole double-throw switches; A resistor attenuation network is used to achieve signal attenuation in an attenuation state; Transmission line used to compensate for the phase difference between a reference path and an attenuated path.

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