WO2009004934A1

WO2009004934A1 - Modulation circuit

Info

Publication number: WO2009004934A1
Application number: PCT/JP2008/061281
Authority: WO
Inventors: Hiroshi Miyagi; Munehiro Karasudani
Original assignee: Nsc Co., Ltd.
Priority date: 2007-07-05
Filing date: 2008-06-13
Publication date: 2009-01-08
Also published as: JP2009017285A

Abstract

Provided a modulation circuit comprising a switch (13) for switching a Q-signal and a QX-signal, which are frequency-offset at a frequency offset unit (23), and a controller (18) for controlling a PC (32) to switch a local oscillation frequency and for controlling the switch (13) to interchange and feed the Q-signal and the QX-signal to a mixer unit (14). In case a local oscillation frequency (Flo) substantially coincident to the frequency of a jamming signal due to a digital signal component is set according to a desired frequency (Fdes) relating to the selection of a user, the local oscillation frequency is changed to leave far the frequency of the jamming signal, thereby to avoid the generation of a beat noise due to the jamming signal and to switch the phase at the time when the frequency mixing is made at the mixer unit (14), so that the frequency position of the image cancellation is changed to a position different from the frequency position of a desired wave signal.

Description

Description Modulation circuit Technical field

The present invention relates to a modulation circuit, and is particularly suitable for use in a circuit for modulating a low frequency signal to a high frequency signal. Background art

In general, in order to transmit information as a radio wave signal, a so-called modulation process that converts a baseband signal (a low-frequency signal including a component near a direct current) into a high-frequency signal is indispensable. Conventionally, when a stereo audio signal is transmitted wirelessly, a frequency modulation method having a strong property against noise on a transmission line has been used in many cases. The frequency modulation method is a method of changing the frequency of a high-frequency signal in proportion to the base spanned signal (FM for analog modulation and FSK for digital modulation).

Normally, in modulation methods that involve frequency conversion, inherently unwanted components such as image noise are generated in a frequency channel (spurious' point) that has a certain frequency relationship with the desired frequency after frequency conversion. There is a problem. In particular, if there is no linearity in the voltage-to-frequency conversion characteristics of the modulator itself, many extra harmonic components appear in the side spur of the desired frequency at the modulation output, and the baseband signal is distorted. It will be equivalent.

However, due to recent developments in digital circuit technology, functions that were previously realized in analog circuits can be realized using digital circuits such as DSP (Digital Signal Processor). Is increasing. The inventor also described In the past, a technique has been proposed in which such frequency modulation processing is performed by a DSP (see, for example, Patent Document 1). In this Patent Document 1, the signal generated by the modulation processing in the baseband frequency domain of the DSP is DZA converted, and this is further modulated into a high frequency signal by analog signal processing. The analog signal processing circuit is integrated into one IC.

Patent Document 1: WO 2 0 0 5 Z 1 2 5 0 2 2

Figure 1 shows the circuit configuration described in Patent Document 1. In the modulation circuit shown in Fig. 1, first, FM modulation by IQ modulation is executed digitally in the baseband region in the quadrature modulation unit 4 in the DSP 100 (frequency from 0 to 75 kHz). Deviation). Next, in the frequency offset unit 5 in D S P 100, a frequency offset (for example, 300 kHz) is digitally added to the I signal and the Q signal. Furthermore, the desired frequency signal of the high frequency (transmission frequency band) is obtained by mixing up the frequency of the frequency offset signal with mixer 6 of the analog circuit.

As is well known, high-frequency analog signal processing circuits and digital signals such as DSP, etc. In an analog-digital mixed IC that integrates a processing circuit into a single chip, the digital signal component affects the analog circuit, so that various characteristics can be obtained. It is easy to get worse. In the case of a modulation circuit such as that shown in Fig. 1 composed of analog-digital mixed IC, most of the deterioration in characteristics occurs in the local oscillation circuit (LOSC) of synthesizer 8 in the analog circuit.

This is because the oscillation circuit has a negative resistance characteristic and has a large gain at the oscillating frequency, so that the oscillation signal is greatly affected even by a minute disturbance signal. For this reason, when the oscillation circuit receives disturbance (interference signal) due to digital signal components, the oscillation signal is re-modulated. This may cause beat noise, and adversely affect the signal at the desired frequency, for example, by deteriorating the S / N ratio or increasing the distortion rate.

FIG. 2 is a diagram showing a spectrum of a desired frequency Fdes, a local oscillation frequency Flo, and an image frequency Fira obtained when the modulation circuit is configured as shown in FIG. When the offset だけ is applied by a predetermined frequency in the frequency offset section 5 in Fig. 1, the local oscillation frequency Flo is set at a position shifted downward by a predetermined frequency ΔF with respect to the desired frequency Fdes. The In this case, the mixer 6 obtains a signal of the desired frequency Fdes by mixing up the baseband frequency offset by a predetermined frequency from the local oscillation frequency Flo.

When the local oscillation frequency Flo is set at a position shifted from the desired frequency Fdes, the image frequency F im ( Image signal) is generated. However, since this image signal is reduced by the image canceller function of mixer 6, the noise level is reduced, which is a practical problem. Disclosure of the invention

However, if the frequency of the interference signal due to the digital signal component matches or is in the vicinity of the local oscillation frequency Flo, the carrier leak and the interference signal cause a bit and bit noise occurs. To the problem of doing.

The present invention has been made to solve such problems, and is intended to reduce the occurrence of bit noise due to an interfering signal without reducing the level of the desired wave signal. Objective.

In order to solve the above problems, the present invention provides an in-phase signal and a quadrature signal. The frequency conversion is performed by adding a predetermined frequency offset to the frequency of the signal, and the in-phase and quadrature signals that have been frequency offset are mixed with the in-phase and quadrature local oscillation signals to obtain the desired frequency signal. Make it happen. In addition, the local oscillation frequency is appropriately switched, and the mixed phase between one of the in-phase signal and the quadrature signal whose frequency is offset and one of the in-phase and quadrature local oscillation signals is appropriately switched. Here, it is preferable to switch the local oscillation frequency and the mixing phase when an interference signal exists in the vicinity of the local oscillation frequency.

According to the present invention configured as described above, when the frequency of the interference signal due to the digital signal component matches or is in the vicinity of the local oscillation frequency, the local oscillation frequency is switched. Since the local oscillation frequency is far from the frequency of the disturbing signal, it is possible to avoid the noise caused by the carrier leak and the disturbing signal being beaten. Also, in this case, by switching the frequency mixing phase in the mixer section, the image cancel frequency position of the image canceller function of the mixer section is changed to a position different from the frequency position of the desired wave signal. Therefore, the inconvenience that the amplitude of the desired signal is suppressed by the image canceller function can be prevented. Brief Description of Drawings

FIG. 1 is a diagram illustrating a configuration example of a conventional modulation circuit.

Figure 2 shows the frequency spectrum obtained by a conventional modulation circuit.

FIG. 3 is a diagram illustrating an example of the overall configuration of the modulation circuit according to the present embodiment. FIG. 4 is a diagram showing a frequency spectrum obtained by the modulation circuit of this embodiment. FIG. 5 is a diagram illustrating another partial configuration example of the modulation circuit according to the present embodiment.

Best Mode for Invention

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a diagram illustrating a configuration example of the modulation circuit according to the present embodiment. Of the components shown in FIG. 3, all the components other than antenna 16 are integrated into one nap by, for example, a CMOS (Complementary Metal Oxide Semiconductor) process.

In Fig. 3, 10 L and 10 R are AZD converters (A DC), which convert the L channel signal and R channel signal input as analog signals into digital signals, respectively.

1 1 is DSP, which performs predetermined digital signal processing on the digital L-channel signal and R-channel signal output from the AZD converters 10 L and 10 R. The DSP 11 includes a signal processing unit 21, an FM modulation unit 22, and a frequency offset unit 23 as functional configurations for performing the digital signal processing. For example, the signal processing unit 21 performs the same processing as the limiter pre-emphasis circuits 1 L and 1 R, the low-pass filters 2 L and 2 R, and the stereo signal generation unit 3 shown in FIG. When done, a stereocomposite signal is generated.

In other words, the signal processing unit 21 performs processing for limiting the amplitude of each of the L channel signal and the R channel signal input as digital signals from the AZD converters 10 L and 10 R. And the signal processing unit 21 performs the processing for emphasizing the modulation factor of the high frequency band (limiter pre-emphasis processing) o and the signal processing unit 2 1 Apply band limitation to (low-pass filter processing). More In addition, the signal processing unit 21 generates a stereo composite signal from the filtered L channel signal and R channel signal (stereo signal generation processing).

The FM modulation unit 22 performs IQ modulation in the baseband frequency range (for example, any power from 0 to 75 kHz) with respect to the stereocomposite signal output from the signal processing unit 21. By applying FM modulation, the in-phase signal (I signal, IX signal) and the quadrature signal (Q signal, QX signal) with a phase orthogonal to it are generated. Here, X indicates that the phase is inverted 180 degrees. That is, the I X signal is a signal in which the phase of the I signal is inverted by 180 degrees, and the Q X signal is a signal in which the phase of the Q signal is inverted by 180 degrees. A specific configuration for generating these in-phase signal and quadrature signal is not shown, but it is possible to apply known signal processing. The frequency offset unit 23 is an FM modulation unit. 22 Frequency conversion is performed by adding a predetermined frequency offset to the frequency of the in-phase and quadrature signals generated by 2. The offset frequency added here is, for example, 300 kHz. As shown in FIG. 3, the frequency offset unit 23 includes a first mixer 23a, a second mixer 23b, and triangular wave generators 23c, 23d.

First mixer 2 3 a in-phase signal (I signal, IX signal) in triangular wave COSC _s t-phase input Ri by triangular wave generator 2 3 c (0 °) sheet off Tosuru frequencies. The second mixer 2 3 b is quadrature signal (Q signal, QX signal) in triangular wave sin co _s t of the triangular wave generator 2 3 d by Ri quadrature input (9 0 °) shifts the frequency of the To do. The frequency of the triangular wave used here is the offset frequency of 300 kHz.

The triangular wave generators 2 3 c and 2 3 d have a frequency of 3 0 0 kHz, for example, Generates in-phase and quadrature triangle waves that are approximately equal in width and out of phase with each other by .90 °, and generates the in-phase triangle wave in the first mixer 2 3 a and the quadrature triangle wave in the second mixer 2 3 Supply to b. The triangular wave generator 2 3 c, 2 3 d may, for example, a sin table information and cos Te one table information, and generates the triangular wave of the triangular wave and sino _s t of cosw _s t using these table information.

Next, 1 2 1 and 1 2 Q are DZA converters (DACs), which are in-phase signals (I signals, IX signals) and quadrature signals input as digital signals from the frequency offset section 2 3. (Q signal and QX signal) are converted into analog signals.

1 3 is a switch (corresponding to the switching unit of the present invention), and after being frequency offset by the frequency offset unit 2 3, it is converted to an analog signal by the D / A converter 1 2 Q. The switching operation of the output power without changing the orthogonal signal (Q signal and QX signal) as it is, and switching the Q signal and QX signal for output. Details of the switching operation will be described later. In the present embodiment, the I signal and the I X signal are not subject to switching.

14 is a mixer section. 0 Inverter signals (I signal, IX signal) and quadrature signals (Q signal, QX signal) converted to analog signals by 8 converters 1 2 I, 1 2 Q Perform frequency conversion. That is, the mixer unit 14 frequency-mixes the in-phase signal and the quadrature signal that have been frequency-offset by the frequency offset unit 23 and the in-phase and quadrature local oscillation signals to obtain the desired frequency F des (for example, , FM frequency band frequency) signal.

As shown in FIG. 3, the mixer section 14 includes a first mixer 14 a, a second mixer 14 b, a first adder 14 c, and a second adder 14 d. ing. The first mixer 1 4 a is the I signal supplied from the D-no A converter 1 2 1 Is modulated by the in-phase (0 °) carrier coso ^ t and the result is output to the first adder 14c. The first mixer 14 a also modulates the IX signal supplied from the D / A converter 1 2 I power with the in-phase (0 °) carrier _COS CO _e t, and the result is added to the second sum 1 4 Output to 4d.

The second mixer 1 4 b modulates the Q signal (or QX signal) supplied from the D / A converter 1 2 Q through the switch 1 3 with a quadrature (90 °) carrier sinwct, The result is output to the first adder 1 4 c. The second mixer 14 b also converts the QX signal (or Q signal) supplied from the 0-8 converter 1 2 Q through the switch 13 to the quadrature (90 °) carrier si η ω _c t. Modulate and output the result to the second adder 14 d.

The first adder 14 4 c combines the I signal and Q signal (or QX signal) modulated by the mixers 14 4 a and 14 b, and the first stereo FM modulated signal having the desired frequency Fdes. And output. The second adder 14 d combines the IX signal modulated by the mixers 14 a and 14 b and the QX signal (or Q signal) to generate the second stereo FM modulated signal having the desired frequency Fdes. As output. The first stereo FM modulation signal and the second stereo FM modulation signal are signals whose phases are inverted by 180 degrees.

A power amplifier 15 amplifies the stereo FM modulation signal output from the mixer section 14 and transmits it via the antenna 16. This power amplifier 1

5 may be a single amplification type or a differential amplification type. In the case of a single amplification type, for example, only the first stereo FM modulated signal output from the first adder 14 c of the mixer unit 14 c is input and amplified (second adder 1 (The second stereo FM modulation signal output from 4d is not used.) In the case of the differential amplification type, the mixer section 14 outputs the second and second stereo FM modulation signals. Amplify by differential input. 1 7 is a synthesizer section. Two mixers 1 in mixer section 1 4

Generates local oscillation signal (carrier wave) to be supplied to 4a and 14b. Ie

The synthesizer unit 17 generates in-phase and quadrature carriers whose amplitudes are substantially equal and whose phases are 90 ° apart from each other.

In 4a, an orthogonal carrier wave is supplied to the second mixer 14b. In this embodiment, the synthesizer unit 17 has a function of switching the local oscillation frequency Flo of the carrier wave.

Specifically, the synthesizer section 17 includes a PLL (Phase Locked Loop) circuit comprising a local oscillator (LOSC) 3 1, a programmable counter (PC) 3 2, a phase detector 3 3 and an LPF 3 4 force, 1 1: A frequency divider 3 5 and a ring oscillator 3 6, 3 7 are provided. Here, the local oscillation supplied from the synthesizer section 17 to the mixer section 14 is made variable by changing the value N of the division ratio setting signal for the PC 3 2 (hereinafter referred to as the program count value N). The local oscillation frequency Flo of the signal (carrier wave) can be switched.

Note that the configuration for making the local oscillation frequency F lo variable is as described above.

The configuration is not limited to using P C 3 2. For example, as shown in Figure 1, for a synthesizer, coil L, variable capacitance diode D

It is also possible to connect the load capacitance value changing unit consisting of 1 and the capacitor C 1 and use the variable capacitance diode D 1 to variably control the frequency of the carrier wave generated by the synthesizer.

Reference numeral 18 denotes a controller (corresponding to the control unit of the present invention), which controls the PC 32 to switch the local oscillation frequency Flo of the local oscillation signal generated by the synthesizer unit 17. That is, when the user operates a channel operation unit (not shown) to instruct switching of the desired frequency Fdes, the controller 18 receives this instruction and is required to obtain the instructed desired frequency Fdes. In order to generate a local oscillation signal with the required local oscillation frequency Flo, the program count value N set for PC 3 2 is changed to a value that matches the desired frequency Fdes.

In addition, the controller 18 controls the PC 3 2 to change the local oscillation frequency Flo according to the set value of the desired frequency Fdes, and the Q signal and QX signal whose frequency is offset. Switch 13 is controlled so that the mixed phase of the signal and the local oscillation signal is switched. That is, when the program count value N, which is set according to the desired frequency Fdes, and thus the local oscillation frequency Flo, reaches a predetermined value, the frequency of the interference signal generated by the digital signal component inside the chip The local oscillation frequency Flo is almost the same, and the carrier and the disturbing signal generate a bit noise by generating a bit in this way. It is known at the time of chip design whether beat noise is likely to occur when set. Therefore, when setting such a known program count value N to PC 32, the controller 18 further changes the program count value N to disturb the local oscillation frequency Flo. In addition to shifting the frequency from the signal frequency, switching the switch 1 3 switches the Q signal and QX signal that have been offset in frequency, so that the second mixer 1 4 in the mixer section 1 4 Control to supply to b.

Hereinafter, the operation of the controller 18 related to the change of the local oscillation frequency Flo and the switching of the switch 13 will be described in detail. In the initial state, the controller 18 has a local oscillation frequency Flo (first frequency of the present invention) at a position shifted downward by a predetermined offset frequency ΔF with respect to the desired frequency Fdes as shown in FIG. Equivalent to local oscillation frequency). Program count value N of PC 3 2 is set to that value. In this case, the mixer section 1 4 Performs frequency mixing with the lower modulation method. At this time, the frequency position of the image canceling by the mixer section 14 is set to a position shifted downward by 厶 F from the local oscillation frequency Flo, and the image noise generated at the frequency position is mixed. Canceled by. In addition, when the program count value N corresponding to the desired frequency Fdes set by the user is set in the PC 32, the controller 18 is the first set by the program count value N. When the local oscillation frequency Flo of the signal coincides with the known frequency range of the interference signal due to the digital signal component, it is output from the synthesizer unit 17 by changing the setting of the program count value N for PC 3 2. The local oscillation frequency of the local oscillation signal to be switched is switched from the first local oscillation frequency Flo to the second local oscillation frequency Flo ′. For example, as shown in FIG. 4 (a), the local oscillation frequency F lo ′ is set at a position shifted upward by a predetermined offset frequency ΔF with respect to the desired frequency Fdes. In this case, the mixer unit 14 performs frequency mixing processing using the upper modulation method.

In this way, since the local oscillation frequency F lo ′ is far away from the frequency of the interference signal, it is possible to avoid occurrence of beat noise due to the interference signal. However, since the frequency position of the image canceling by the mixer section 14 is set to a position shifted by ΔF from the local oscillation frequency F lo ′, the frequency spectrum as shown in Fig. 4 (a) In the case of a ram, the frequency position of the image cancel by the mixer section 14 overlaps the frequency position of the desired signal. For this reason, the amplitude of the desired signal is suppressed by the image canceller function of the mixer section 14 and the output level is reduced.

Therefore, in this embodiment, not only the local oscillation frequency is switched from F lo to F lo ′ but also the Q signal and the QX signal that are frequency offset are input. Instead, the switch 13 is controlled so as to be supplied to the second mixer 14 b of the mixer unit 14. This switches the mixing phase between the Q and QX signals and the orthogonal local oscillation signal with the local oscillation frequency set to F lo ′. Specifically, switch 1 3 is normally set to terminals a 1 and b 1 side by switching to terminals a 2 and b 2 side. Switching the combination of the I signal and Q signal in c to the combination of the I signal and QX signal, and usually the IX signal and QX signal in the second adder 14 d Is switched so that the IX signal and the Q signal are combined.

In this way, the phase of the quadrature signal input to the mixer section 14 changes by 180 °, so that the frequency position of the image cancel is shifted upward by ΔF from the local oscillation frequency F lo ′. It is possible to prevent the inconvenience that the amplitude of the desired signal is suppressed by being changed. As a result, the frequency spectrum is as shown in Fig. 4 (b). In other words, the signal amplitude at the desired frequency Fdes is increased without being suppressed by the image canceller function. In addition, image noise generated at a position shifted by ΔF from the local oscillation frequency F lo ′ is suppressed.

As described above in detail, in the present embodiment, a predetermined frequency offset is added to the modulation signal generated by the FM modulator 22, and the desired frequency Fdes according to the user selection is added. When the local oscillation frequency Flo that matches the frequency range of the interference signal due to the digital signal component is set, the local oscillation frequency is switched to another frequency Flo 'and the frequency offset unit 2 3 The output DZ A converter 1 2 The Q signal and the QX signal converted into analog signals are interchanged and supplied to the second mixer 1-4 b of the mixer section 14.

With this configuration, the frequency of the disturbing signal matches the local oscillation frequency. If it exists in the vicinity, the local oscillation frequency will be changed and it will be far from the frequency of the interfering signal, thus avoiding the noise generated by the carrier leak and the interfering signal being beaten. Can do. In this case, by switching the frequency mixing phase in the mixer section 14, the frequency position of the image cancellation in the mixer section 14 is changed to a position different from the frequency position of the desired signal, The inconvenience that the amplitude of the desired signal is suppressed by the image canceller function can also be prevented. In the above embodiment, the Q signal output from the frequency offset unit 23 and analogized by the DZA converter 12 Q is exchanged with the QX signal and supplied to the first mixer 14 a. However, it is not limited to this example. For example, the I signal and the IX signal output from the frequency offset unit 2 3 and analogized by the DZA converter 1 2 1 may be switched and supplied to the second mixer 14 b. .

Also, as shown in Fig. 5, the Q signal and the QX signal are not interchanged, and the second mixer 14 b is switched by switching the displacement angle of the orthogonal local oscillation signal output from the synthesizer section 17. You may make it supply to. FIG. 5 is a diagram illustrating another configuration example of the modulation circuit according to the present embodiment. Here, only a part of the configuration of the modulation circuit is shown. In the example shown in FIG. 5, the switch 1 3 does not exist between the 0-8 converters 1 2 1, 1 2 Q and the mixer unit 14, and the ring oscillators 3 6, 3 in the synthesizer unit 1 7 Another switch 1 3 is inserted between 7 and the mixer section 14.

As shown in Fig. 5, the oscillators 3 7 on the rear side of the ring oscillators 3 6 and 3 7 are positive oscillators whose phase is shifted by + 90 ° from the in-phase local oscillator signal as an orthogonal local oscillator signal. It outputs a quadrature local oscillation signal and a negative quadrature local oscillation signal that is 90 ° out of phase with the local oscillation signal in phase. Switch 1 3 ′ switches between the positive and negative quadrature local oscillation signals as appropriate to switch the second mixer. 1 4 Supply to b.

That is, when the first local oscillation frequency Flo matches the frequency range of the jamming signal, the controller 18 controls the switch 1 3 ′ and is normally set to the terminal c 1. Switch to the terminal c 2 side. As a result, a positive quadrature local oscillation signal of + 90 ° is normally supplied to the second mixer 14b, but a negative quadrature local oscillation signal of 90 ° is supplied. Try to do so.

In addition, each of the above-described embodiments is merely an example of a specific example for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the spirit or the main features thereof. Industrial applicability

The present invention is useful for a modulation circuit for modulating a baseband signal into a radio high-frequency signal.

Claims

The scope of the claims

1. Modulation unit that generates an in-phase signal and a quadrature signal with a phase orthogonal thereto, and frequency conversion is performed by adding a predetermined frequency offset to the frequency of the in-phase signal and quadrature signal generated by the modulation unit. The frequency offset section to perform,

A mixer unit that generates a signal having a desired frequency by frequency-mixing an in-phase signal and a quadrature signal that have been frequency-offset by the frequency offset unit and an in-phase and quadrature local oscillation signal;

A synthesizer unit that generates the in-phase and quadrature local oscillation signals, and has a function of switching a local oscillation frequency of the local oscillation signal;

Switching to switch the mixed phase between one of the in-phase signal and quadrature signal frequency offset by the frequency offset unit and one of the in-phase and orthogonal local oscillation signal generated by the synthesizer unit And

A control unit that controls the synthesizer unit so as to switch a local oscillation frequency of a local oscillation signal generated in the synthesizer unit, and controls the switching unit so as to switch the mixed phase. Characteristic modulation circuit.

2. The control unit sets the local oscillation frequency of the local oscillation signal to the first local oscillation frequency when the first local oscillation frequency set according to the desired frequency matches the frequency range of the interference signal. 2. The modulation circuit according to claim 1, wherein the synthesizer unit is controlled to switch from the first to the second local oscillation frequency, and the switching unit is controlled to switch the mixed phase. .

3. The first local oscillation frequency is lower than the desired frequency. 3. The modulation circuit according to claim 2, wherein the second local oscillation frequency is higher than the desired frequency.

4. The switching unit is provided between the frequency offset unit and the mixer unit, and has a phase of 1 with respect to the orthogonal signal frequency-offset by the frequency offset unit and the orthogonal signal. The modulation circuit according to any one of claims 1 to 3, wherein the inverted orthogonal signal inverted by 80 degrees is replaced and supplied to the mixer section.

5. The switching unit is provided between the synthesizer unit and the mixer unit, and exchanges the positive orthogonal local oscillation signal and the negative orthogonal local oscillation signal generated by the synthesizer unit to replace the mixer. The modulation circuit according to any one of claims 1 to 3, wherein the modulation circuit is supplied to a part.