JP2008005251A - Oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To logically clarify that oscillation beyond the oscillation limit of a capacitative circuit is possible, and to provide a concrete circuit example. <P>SOLUTION: This oscillation circuit includes a piezoelectric oscillator with capacitors serially connected thereto; an invertor connected in parallel with the piezoelectric oscillator; and a transistor whose base is connected to the output terminal of the inverter wherein a resistance is connected between the input terminal and output terminal of the invertor, and a capacitor is connected between the input terminal and ground of the invertor, and a capacitor is connected between the base and emitter of the transistor, and a resistor is connected between the emitter and ground of the transistor, and the parallel circuit of the capacitor is connected between the emitter and ground of the transistor, and a resistor is connected between the collector and power source of the transistor, and the power supply terminal of the invertor is connected to the power source, and a ground terminal is connected to the ground, and a path capacitor is connected between the power source and the ground, and the collector of the transistor is defined as an output. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oscillator used for detection of chemical and medical information such as carbon dioxide, dioxin, and bio, and an oscillator used for reference oscillation of mobile communication or wired communication by a QCM (quartz microbalance for measuring minute mass). This is applied to the oscillation circuit.

As represented by Colpitts shown in Fig. 31 (a), the conventional oscillation circuit is composed of a piezoelectric vibrator, active element, resistor, and capacitor, and the equivalent circuit excluding the vibrator when starting oscillation is a negative resistance. (= Rci) and capacitive reactance (= Cci) are shown in series connection (for example, see Non-Patent Document 1). In addition, the equivalent circuit of the vibrator has the same capacity as the motion arm circuit indicated by the series connection of inductive reactance (= L1), capacitive reactance (= C1), and resistance (= R1), and the capacitance between electrodes (= C0). It can be equivalent to the capacitance including the parasitic capacitance (= Cα) connected in parallel. An equivalent circuit is shown in FIG. The combined impedance of the capacitance (= Cα) and Rci · Cci is obtained, and the resistance is represented by Rcci and the capacitive reactance is represented by Ccci, respectively.

  FIG. 33 and FIG. 34 show the simulation results of equation (2). Figure 33 shows a fixed frequency (Freq = 10MHz) and circuit capacitance (Cci = 30pF), with the interelectrode capacitance (= C0) and the parasitic capacitance combined capacitance (Cα) as parameters, and the negative resistance of the circuit (-Rci) , Negative resistance (Rcci) that promotes oscillation start, and capacitive reactance (Ccci) of the circuit. It can be seen that the negative resistance Rcci has a maximum value, and that value is related to the combined capacitance Cα.

  Similarly, in Fig. 34, the frequency (Freq = 10MHz) and the combined capacitance (C0 + Cα = 10pF) are fixed, the circuit capacitance (= Cci) is used as a parameter, the negative resistance (−Rci) of the circuit and the negative value that starts oscillation The relationship between the resistance (Rcci) and the capacitive reactance (Ccci) of the circuit is shown. As in FIG. 33, it can be seen that the negative resistance Rcci has a maximum value, and that value is related to the circuit capacitance Cci.

The maximum value of Rcci is obtained from equation (7) to obtain equation (3).

From the equation (3), the maximum value of Rcci strongly depends on the value of Cα, and further shows the maximum value from Cci → infinity.

  Equation (4) shows the limit of the negative resistance Rcci when the circuit reactance is capacitive.

  FIG. 35 shows the limit values of Cα and RcciMax. For example, when Cα = 10 pF, RcciMax = −0.8 kΩ is shown. If the reactance of the oscillation circuit is capacitive, it is impossible to oscillate a vibrator having a series resistance of 0.8 kΩ.

In addition, as an oscillation circuit using an inductor (coil), an inductor (extension coil) is inserted in series with the vibrator in the Hartley oscillation circuit shown in Fig. 31 (b) or the Colpitts oscillation circuit shown in Fig. 31 (c). However, there is a method of making the circuit excluding the vibrator inductive (for example, see Non-Patent Document 2). FIG. 36 shows an equivalent circuit of the circuits (b) and (c). In the Hartley oscillation circuit of (b), an unnecessary oscillation loop is configured by a loop composed of parallel capacitors of L2, C1, and the resonators C0 and Cα, and oscillation starts when a negative resistance occurs in the circuit. The oscillation frequency is given by equation (5).

In the Colpitts oscillation circuit with an extension coil shown in (c), an unnecessary oscillation loop is formed by a loop composed of L, C1, C2, and the parallel capacitance of C0 and Cα of the oscillator, and oscillation occurs if a negative resistance occurs in the circuit. to start. The oscillation frequency is approximately given by equation (6).

That is, an inductor (coil) is inserted into an oscillation circuit with a piezoelectric oscillator to form an oscillation circuit, and the reactance on the circuit side is inductive, because unnecessary oscillation is induced by the inserted inductor. An inductor may be inserted in some high-frequency oscillations, but an inductor having a value large enough to make the reactance on the circuit side inductive is not inserted, and the reactance on the circuit side is limited to a capacitive range.
Artificial quartz and its electrical application, supervised by Sadao Taki Tiger technique ORIGINAL No.8, transistor technology editorial department

  When an oscillation circuit is configured by inserting an inductor into the piezoelectric oscillation circuit, unnecessary oscillation is started by the insertion inductor. Therefore, it is possible to oscillate beyond the oscillation limit of the capacitive circuit by configuring the oscillation circuit with active elements, resistors, and capacitors, and making the reactance of the circuit excluding the vibrator inductive without using an inductor. Theoretical clarification and specific circuit examples are provided.

  First, it will be shown that by making the reactance of the circuit excluding the vibrator inductive, it is possible to obtain an advantage superior to the capacitive oscillation of a circuit typified by a conventional Colpitts type. Next, it is shown that the reactance of the circuit can be made inductive only by using a resistor, a capacitor, and an active element without using an inductor.

Fig. 1 shows an inductive oscillation equivalent block of the invention. The equivalent inductive reactance: Lci shown in Fig. 1 is composed of active elements, resistors, and capacitors. FIG. 1 can be equivalent to FIG. 2 (a) or (b). Fig. 2 (a) shows the capacitance between the electrodes in Fig. 1: Parasitic capacitance in parallel with the same capacitance as C0: Cα is combined with the equivalent inductive reactance of the circuit: Lci and negative resistance: Rci, equivalent resistance: Rcci Capacitive reactance: Ccci, which forms an oscillation loop with motion arms L1, C1, and R1. Fig. 2 (b) shows the capacitance between the electrodes shown in Fig. 1: Parasitic capacitance in parallel with the same capacitance as C0: Cα is combined with the equivalent inductive reactance: Lci and negative resistance: Rci of the circuit, and equivalent resistance: Rcci. Inductive reactance: Lcci, which forms an oscillation loop with motion arms L1, C1, and R1. Equivalent resistance: Rcci, capacitive reactance: Ccci, and inductive reactance: Lcci shown in FIGS. 2 (a) and (b) are shown in equation (7).

  Figure 3 shows the simulation result of equation (7). Negative resistance: Rcci = 1kΩ, Inductive reactance: Lci = 25.53μH, Interelectrode capacitance and parasitic capacitance: C0 + Cα = 10pF, Resonance frequency of Lci and C0 + Cα: fα = 10MHz, Frequency and resistance: Rcci, The relationship between capacitive reactance: Ccci and inductive reactance: Lcci is shown. Rcci shows a maximum value of −2.8 kΩ at 9 MHz, shows inductive reactance at about 8 MHz or less, and shows capacitive reactance at about 8 MHz or more. Fig. 4 shows C0 + Cα = 10pF, Lci is the inductive reactance that resonates at the same capacity and 10MHz (here, Lci ≒ 25.3μH), and the negative resistance Rci of the circuit excluding the oscillator is used as a parameter, and frequency, Rcci, Ccci The relationship is shown. That is, it is understood that the negative resistance: Rcci has a maximum value near the resonance frequency, and that the capacitive reactance Ccci has a large capacity at the maximum value of resistance. Moreover, it can be seen that the maximum value of Rcci increases as the negative resistance of Rci decreases.

  FIG. 5 shows the relationship between frequency, Rcci, and Ccci with negative resistance Rci = 1 kΩ, Lci as the inductive reactance that resonates at the same capacity and 10 MHz, and C0 + Cα as a parameter. FIG. 37 shows the maximum value of the negative resistance at that time.

  That is, it is understood that the negative resistance: Rcci has a maximum value near the resonance frequency, and that the capacitive reactance Ccci has a large capacity at the maximum value of resistance. Moreover, it can be seen that the maximum value of Rcci increases as the capacity of C0 + Cα decreases.

  Next, an example of an oscillation circuit that generates an inductive reactance without using an active element, a resistor, and a capacitor without using an inductor in the oscillation circuit will be described.

Example 1
Fig. 6 shows an inductive piezoelectric oscillation model-1 circuit using an inverter and a bipolar transistor. The resistor R1 is inserted between the input and output of the inverter, and sets the input bias of the inverter and the base bias of the transistor. R2 is input between the collector of the transistor and the power supply to obtain an oscillation output. R3 is inserted between the emitter of the transistor and the ground to set the transistor current. Capacitor C1 is inserted between the inverter input and ground, C2 is inserted between the base and emitter of the transistor, and C3 is inserted between the emitter of the transistor and ground. Figure 7 shows the equivalent circuit. z1, z2, z3 and z4 indicate the impedances of the respective two-terminal circuits. Kirchoff's law is applied to the figure, and Equations (8) and (9) are obtained from the current relationship, and Equation (10) is obtained from the voltage relationship.

Equation (11) is obtained from Equations (8) to (10).

Further, R1 and the oscillator impedance zxt are separated, and the equation (12) indicating the impedance of the oscillation circuit excluding zxt is obtained.

The two-terminal impedances z1, z2, and z3 are set as shown in equation (13) and assigned to equation (12).

Let Rci be the resistance of the oscillation circuit excluding the oscillator (zxt), and Lci be the inductive reactance.

Further, the resistance Rc and the inductive reactance Lc are expressed by the equation (15), respectively.

  Figure 8 shows the simulation result of equation (15). C1 = 3pF, C2 = C3 = 15pF, Cπ = 1pF, Rπ = 2.6kΩ, R1 = 1MΩ, R3 = 2kΩ, gm1 = 1mA / V, gm2 = parameter, frequency and circuit resistance Rci and inductive reactance Lci of the circuit The relationship is shown.

  It can be seen that both Rci and Lci strongly depend on the frequency. Also, gm2 depends strongly, but increasing gm2 does not increase unidirectional for both Rci and Lci. From this graph, Rci increases with decreasing gm2. Also. Lci obtains the maximum value (Lci≈80mH) at gm2 = 76mA / V and frequency (Freq) ≈7MHz.

  Using the above theory, Figure 6 circuit, Figure 11 circuit in which the inverter and transistor Vcc are separated, Figure 12 circuit in which the resistor is added to the inverter in Figure 11 circuit, and resistance is added to the inverter in Figure 6 circuit The circuit shown in FIG. 13 is obtained. In addition, a circuit in which two transistors of these circuits are cascode-connected is obtained. FIG. 29 is a circuit example in which two transistors in FIG. 6 are cascode-connected.

Example 2
Figure 9 shows an inductive piezoelectric oscillation model-2 circuit using an inverter and a bipolar transistor. The resistor R1 is inserted between the input and output of the inverter, and sets the input bias of the inverter and the base bias of the transistor. R2 is input between the collector of the transistor and the power supply to obtain an oscillation output. R3 is inserted between the emitter of the transistor and the ground to set the transistor current. Capacitor C1 is inserted between the inverter input and ground, C2 is inserted between the base and emitter of the transistor, and C3 is inserted between the emitter and ground of the transistor. FIG. 10 shows the equivalent circuit. z1, z2, z3 and z4 indicate the impedances of the respective two-terminal circuits. Applying Kirchoff's law to the figure, we obtain Eqs. (16) and (17) from the current relationship, and (18) from the voltage relationship.

  Substitute (16) and (17) into (18) and rearrange them to obtain (19).

  Equations (19) and (11) are equivalent. Therefore, the results after the equation (19) are the same as the equations (12) to (15), that is, the simulation result of FIG.

  Using the above theory, the circuit shown in Fig. 9, the inverter shown in Fig. 9 separated from the Vcc of the transistor, the circuit shown in Fig. 15 added with the inverter in Fig. 14 and the resistor added to the inverter shown in Fig. 9 were added. The circuit shown in FIG. 16 is obtained. In addition, a circuit in which two transistors of these circuits are cascode-connected is obtained. FIG. 30 is a circuit example in which two transistors in FIG. 9 are cascode-connected.

  The present invention can contribute to diversification of QCM sensors as oscillation of a piezoelectric element having a large mechanical load. Further, according to the present invention, it is possible to easily enable a QCM sensor in a liquid phase (measurement of a very small amount by a crystal resonator). As a result, the present invention is a technology that can be widely applied to actuators using various piezoelectric elements and greatly contributes to future technological development.

(Example 1)
FIG. 17 shows the first embodiment of the oscillation circuit according to the present invention. Setting constants are C1 = 3pF, C2 = 15pF, C3 = 15pF, Cpi = 1pF, Rpi = 2.6kOhm, R3 = 2kOhm, R1 = 1Mohm, Cp1 = 220pF, INV: TC7SU04F, TR1: 2SC3732, Zxt (Xtal): At -cut 10MHz.

  FIG. 18 shows power supply voltage versus oscillation frequency and current consumption characteristics. FIG. 18 shows the measurement of frequency and current consumption when the power supply voltage of the circuit of FIG. 17 is changed using the above set constant. In particular, it was confirmed that it oscillates reliably to VCC: 5.5V.

  FIG. 19 shows the series capacitance of the vibrator when VCC = 4V: Cx vs. oscillation frequency characteristics. FIG. 19 shows a change in frequency caused by operating Cx when the power supply voltage VCC of the circuit of FIG. 17 using the above set constant is set to 4V. As the frequency variable range, a variable range of Δf / f0≈380 ppm was confirmed.

(Example 2)
FIG. 20 shows a second embodiment of the oscillation circuit according to the present invention. Setting constants are C1 = 3pF, C2 = 15pF, C3 = 15pF, Cpi = 1pF, Rpi = 2.6kOhm, R3 = 2kOhm, R1 = 1Mohm, Cp1 = 220pF, INV: TC7SU04F, TR1: 2SC3732, Zxt (Xtal): At -cut 10MHz.

  FIG. 21 shows the power supply voltage versus the oscillation frequency when VCC2 = 2V. FIG. 21 shows the measurement of frequency change when the power supply voltage VCC1 of TR1 of the circuit of FIG. 20 using the above set constant is changed. In particular, it was confirmed that it oscillates reliably to VCC1: 10V.

  FIG. 22 shows the series capacitance of the vibrator: Cx vs. oscillation frequency when VCC1 = 7V and VCC2 = 4V. FIG. 22 shows the change in frequency caused by operating Cx when the power supply voltage VCC1 = 7V and VCC2 = 4V of the circuit of FIG. A variable range of Δf / f0≈650 ppm was confirmed as the frequency variable range.

(Example 3)
FIG. 23 shows a third embodiment of the oscillation circuit according to the present invention. Setting constants are C1 = 3pF, C2 = 15pF, C3 = 15pF, Cpi = 1pF, Rpi = 2.6kOhm, R3 = 2kOhm, R1 = 1Mohm, Cp1 = 220pF, R4 = R5 = 750kOhm, INV: TC7SU04F, TR1: 2SC3732, Zxt (Xtal): At-cut 10 MHz.

  FIG. 24 shows the power supply voltage versus the oscillation frequency when VCC2 = 4V. FIG. 24 shows the measurement of frequency change when the power supply voltage VCC1 of TR1 of the circuit of FIG. 23 is changed using the above set constant. In particular, it was confirmed that it oscillates reliably to VCC1: 10V.

  FIG. 25 shows characteristics of the series capacitance of the vibrator: Cx vs. oscillation frequency when VCC1 = 7V and VCC2 = 4V. FIG. 25 shows the change in frequency caused by operating Cx when the power supply voltage VCC1 = 7V and VCC2 = 4V in the circuit of FIG. 24 using the above set constants. A variable range of Δf / f0≈670 ppm was confirmed as the frequency variable range.

(Example 4)
FIG. 26 shows a fourth embodiment of the oscillation circuit according to the present invention. Setting constants are C1 = 3pF, C2 = 15pF, C3 = 15pF, Cpi = 1pF, Rpi = 2.6kOhm, R3 = 2kOhm, R1 = 1Mohm, Cp1 = 220pF, INV: TC7SU04F, TR1: 2SC3732, Zxt (Xtal): At -cut 10MHz.

  FIG. 27 shows power supply voltage versus oscillation frequency and current consumption characteristics. FIG. 27 shows the measurement of frequency and current consumption change when the power supply voltage of the circuit of FIG. 26 using the above set constant is changed. In particular, it was confirmed that it oscillates reliably to VCC: 7V.

  FIG. 28 shows the series capacitance of the vibrator when VCC = 5 V: Cx vs. oscillation frequency characteristics. FIG. 28 shows a measurement of frequency change by operating Cx when the power supply voltage VCC of the circuit of FIG. 26 using the above set constant is set to 5V. A variable range of Δf / f0≈200 ppm was confirmed as the frequency variable range.

  This result is compared with capacitive oscillation represented by Colpitts type oscillation circuit.

  The limit value of capacitive oscillation shown in FIG. 34 is compared with the inductive oscillation simulation result of FIG.

  Obviously, a negative resistance Rcci with a large inductive oscillation can be obtained. Moreover, the results in FIG. 33 also indicate that a larger Rcci can be obtained by reducing the negative resistance of Rci.

  In other words, by setting the reactance of the oscillation circuit excluding the vibrator to inductivity without using an inductor (coil), a negative resistance for canceling the resistance in the motion arm constituting the vibrator is capacitively oscillated. You can cancel beyond the limit.

  This can contribute to diversification of QCM sensors as oscillation of piezoelectric elements with a large mechanical load.

  The QCM is a sensor that extracts a change in resonance frequency caused by the detection target substance adhering to the crystal resonator as a change in frequency of the oscillation circuit. QCM is used as a gas phase substance detection technology, and liquid phase substances can be detected in principle, but oscillation is very difficult due to the effect of liquid viscosity. However, according to the present invention, it is possible to easily enable a QCM sensor in a liquid phase (a very small amount measurement using a crystal resonator). The present invention is a technology that can be widely applied to actuators using various piezoelectric elements, and will greatly contribute to future technological development.

It is a circuit diagram which shows the equivalent circuit of invention inductive piezoelectric oscillation model-1. It is a circuit diagram which shows the equivalent circuit of invention inductive piezoelectric oscillation model-2. It is a graph which shows invention inductive piezoelectric oscillation model simulation result-1. It is a graph which shows invention inductive piezoelectric oscillation model simulation result-2. It is a graph which shows invention inductive piezoelectric oscillation model simulation result-3. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-1. It is a circuit diagram which shows the equivalent circuit of invention inductive piezoelectric oscillation model-1. It is a graph which shows the simulation result of invention inductive piezoelectric oscillation model-1. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-2. It is a circuit diagram which shows the equivalent circuit of invention inductive piezoelectric oscillation model-2. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-3. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-4. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-5. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-6. It is a circuit diagram which shows the circuit of invention inductive piezoelectric oscillation model-7. FIG. 6 is a circuit diagram showing a circuit of an inductive piezoelectric oscillation model-8. It is a circuit diagram which shows the implementation circuit of invention inductive piezoelectric oscillation model-1. Fig. 3 is a graph showing an implementation circuit of the invention inductive piezoelectric oscillation model-1 showing power supply voltage vs. oscillation frequency and current consumption. It is a graph which shows the implementation circuit of invention inductive piezoelectric oscillation model-1 variable capacitance (= Cx) vs. oscillation frequency. It is a circuit diagram which shows the implementation circuit of invention inductive piezoelectric oscillation model-3. It is a graph which shows the implementation circuit of invention inductive piezoelectric oscillation model-3 power supply voltage (VCC1) variable vs. oscillation frequency. It is a graph which shows the implementation circuit of invention inductive piezoelectric oscillation model-3. Variable capacity (= Cx) vs. oscillation frequency. It is a circuit diagram which shows the implementation circuit of invention inductive piezoelectric oscillation model-4. It is a graph which shows power supply voltage (VCC1) variable vs. oscillation frequency in the implementation circuit of invention inductive piezoelectric oscillation model-4. It is a graph which shows the variable capacity (= Cx) vs. oscillation frequency in the implementation circuit of invention inductive piezoelectric oscillation model-4. It is a circuit diagram which shows the implementation circuit of invention inductive piezoelectric oscillation model-2. It is a graph which shows the power supply voltage vs. oscillation frequency and current consumption in the implementation circuit of invention inductive piezoelectric oscillation model-2. It is a graph which shows the variable capacity (= Cx) vs. oscillation frequency in the implementation circuit of invention inductive piezoelectric oscillation model-2. It is a circuit diagram which shows the example of the cascode connection circuit of invention inductive piezoelectric oscillation model-1. It is a circuit diagram which shows the example of the cascode connection circuit of invention inductive piezoelectric oscillation model-2. It is a circuit diagram which shows the basic type of a piezoelectric oscillator. It is a circuit diagram which shows the equivalent circuit of a capacitive piezoelectric oscillation circuit. It is a graph which shows the simulation result-1 of a capacitive piezoelectric oscillation circuit. It is a graph which shows the simulation result-2 of a capacitive piezoelectric oscillation circuit. It is a table | surface which shows the limit value of capacitive piezoelectric oscillation. It is a circuit diagram which shows the equivalent circuit of an inductor insertion inductive piezoelectric oscillation circuit. It is a table | surface which shows the comparison of capacitive oscillation and inductive oscillation.

Claims (7)

In an oscillation circuit including a piezoelectric vibrator, an active element, a resistor, and a capacitor,
A circuit composed of the active element, the resistor, and the capacitor is represented as an equivalent circuit by inductive reactance (= Lci) and negative resistance (= Rci), and the piezoelectric vibrator is represented by inductive reactance (= L1), capacitance Motion arm circuit in which a reactive reactance (= C1) and a resistor (= R1) are connected in series, an interelectrode capacitance (= C0) connected in parallel to the motion arm circuit, and a parasitic capacitance (= Cα) in the interelectrode capacitance ) In the capacity including
An oscillation circuit characterized in that the oscillation condition is approximated by the following equation.
An oscillation circuit including a piezoelectric vibrator having a capacitor connected in series, an inverter connected in parallel to the piezoelectric vibrator, and a transistor having a base connected to an output terminal of the inverter,
A resistor is connected between the input terminal and the output terminal of the inverter, and a capacitor is connected between the input terminal of the inverter and the ground,
A capacitor is connected between the base and emitter of the transistor, a resistor is connected between the emitter and ground of the transistor, and a parallel circuit of a capacitor is connected between the emitter and ground of the transistor. A resistor is connected between
The inverter power supply terminal is connected to the power supply, the ground terminal is connected to the ground,
Between the power source and the ground, a pass capacitor that is short-circuited with respect to alternating current and open with respect to direct-current is connected,
An oscillation circuit characterized in that a collector of the transistor is used as an output.   3. The oscillation circuit according to claim 2, wherein a power source of the inverter and a power source of the transistor are different power sources.   4. The oscillation circuit according to claim 2, wherein resistors are connected between a power supply terminal of the inverter and the power supply of the inverter and between a ground terminal of the inverter and the ground, respectively.   3. The oscillation circuit according to claim 2, wherein an input terminal of the inverter is connected to a base of the transistor, a collector of the transistor is used as an output, and an output terminal of the inverter is used as an output. The transistor is
A lower transistor with an inverter output connected to the base;
An upper stage transistor to which an appropriate voltage is applied from the power source of the transistor to the base is configured by cascode connection,
5. The pass capacitor that is short-circuited with respect to alternating current and open with respect to direct-current is connected between the base of the upper stage transistor and the ground. 6. Oscillator circuit. The transistor is
A lower transistor with an inverter output connected to the base;
An upper stage transistor to which an appropriate voltage is applied from the power source of the transistor to the base is configured by cascode connection,
6. The oscillation circuit according to claim 2, wherein a pass capacitor is connected between the base of the upper stage transistor and the ground.