CN1158823C - High-speed power-saving coding M-element FSK modulator - Google Patents

Abstract

A high-speed power-saving encoded M-ary frequency shift keying (frequence shift keying) modulator is provided. The modulator comprises a coding unit, which can generate M/2 gray code signals according to an (N-1) bit control signal and also receive an enabling signal, wherein the coding unit outputs a 0 signal when the enabling signal does not act; and M/2 switch-mode oscillation circuits. Each switch type oscillation circuit comprises a composite quartz resonator with a first end and a second end respectively; a first switch controlled by a gray code signal; a second switch controlled by the serial data; and a capacitor. One of the M/2 switch-type oscillation circuits is controlled to operate by the control signal, and the frequency of the oscillation circuit of the operation is jumped by the serial data, so as to achieve M-element frequency jump.

Description

High-speed power-saving coded M-element FSK modulator

technical field

The invention relates to a frequency shift keying (frequency shift keying, FSK) modulator, in particular to a high-speed power-saving coded M-element FSK modulator suitable for circuit integration.

Background technique

The rapid development of wireless communication technology and the continuous progress of semiconductors make wireless communication technology more widely used in every corner of life. In addition to the familiar cordless phone, cellular phone, pager, car alarm, etc., all kinds of wireless products are spreading to human daily life at an unprecedented speed. in life. This continuous development trend makes radio products not only light, thin, short, and small, but also must realize the following circuit functions at a very low cost: (1) low power consumption, (2) high power Transmission power, (3) high-sensitivity receiving capability, (4) anti-jamming capability. Satisfying the above conditions can not only achieve high-quality radio transmission, but also prolong battery life and meet environmental protection requirements. Accordingly, the inventor adopts the known M-element FSK (M-element frequency shift keying) modulation technology to design a new type of M-element FSK modulator, and utilizes the innate anti-interference ability of FSK to complete low-cost, high-speed switching and changing frequency , and M-element FSK modulator with high efficiency (DC-to-RF output power).

The known and commonly used FSK modulation technology can be summarized into the following methods: phase-locked-loop (phase-locked-loop, PLL) electronic technology, microwave electromagnetic induction technology, digital direct synthesizer (Direct digital synthesis, DDS), And electronic control of the resonator (resonator) technology.

The principle of phase-locked loop electronic technology is to use the output signal of the voltage-controlled oscillator in the loop to compare the phase difference with a phase comparator (phase comparator) and a very stable signal source after passing through several frequency division circuits. The output signal of the phase comparator is properly processed by a low-pass filter to generate a slowly changing signal close to direct current to control the output frequency of the voltage-controlled oscillator. With the action of the negative loop circuit, the voltage controlled oscillator can adjust the frequency of the voltage controlled oscillator according to the setting of the frequency divider. This digital setting can use the input electronic code to generate FSK frequency hopping signal. The biggest disadvantage of this kind of FSK signal generated by PLL is that its frequency hopping rate is limited by the time constant of the filter of the PLL loop. For example, if the channel spacing of the FSK signal is 200KHz, in order to correctly and accurately modulate the FSK signal, a typical PLL loop time constant needs about 0.5ms, so that the FSK signal can change (frequency hop) to the specified frequency. This greatly limits the FSK frequency hopping rate, and at this time the typical loop bandwidth (loop bandwidth) is 16.5KHz, which is much greater than the data rate (data rate) of FSK. Therefore, the PLL at this time can correctly and accurately modulate the FSK signal. However, the data rate in this case is quite slow, and the frequency spacing of 200KHz cannot be fully utilized, so the utilization rate of the channel is greatly reduced.

Secondly, microwave electromagnetic induction technology uses PIN diodes (diodes) or varactor diodes (varactor diodes), through switching action or capacitance changes, through electromagnetic induction, the impedance change is converted to the oscillator circuit, and then the oscillation of the oscillator is adjusted. Oscillating conditions such that the frequency therefore varies with the signal controlling the PIN diode or varactor. The advantage of this approach is that the ratio of the switchable frequency (Δf) to fo (Δf/fo) can be small, and the switching rate is very fast. The disadvantage is that the electromagnetic circuit is not easy to achieve circuit integration, because the size and the wavelength of the operating frequency are close, so the area is relatively large, and a hybrid (Hybrid) MIC is often required for implementation. In addition to using voltage-controlled varactor diodes, the method of using the switching action of PIN diodes to control the frequency of the resonant cavity is also widely used. When the switching action of the PIN diode is turned on (non-conducted), part of the inductance or capacitance in the resonant cavity can be connected (not connected), thereby changing the output frequency of the oscillator. However, switching circuits using PIN diodes still need to consume extra DC current to achieve the on-state, and the form of PIN diodes is not suitable for importing into today's common IC forms such as CMOS, bipolar, or GaAs FET.

Furthermore, the digital direct synthesizer uses a digital IC to operate a digital accumulator (digital accumulator) in a high-speed clocked condition, and at the same time converts the output signal waveform to be generated, such as a sine wave (sine wave) wave) or any composite signal (composite signal) phase data stored in ROM. Taking the sine wave output as an example, the digital accumulator outputs the appropriate digital code to the input terminal of the digital-to-analog converter (DAC) according to the specified frequency, generates the desired analog waveform, and filters it out through the anti-aliasing filter . The M-element FSK signal synthesized by this digital IC needs to use VLSI technology, so the power consumed is usually very large, and it loses its advantages when the power consumption must be limited.

Finally, the technique of electronically controlling the resonant cavity reduces an oscillator to the circuit shown in Figure 5. The part of the oscillator that can provide an amplified signal is represented by a negative impedance (-R), while the part that performs vibration modulation still uses a parallel Rr-Cr-Lr circuit to represent a parallel resonant cavity for vibration modulation. Among them, Rr represents the loss of the resonant cavity, and the larger the Rr, the lower the loss. Therefore, Rr>|-R| can start the oscillation. Changing the value of Lr and Cr can change the oscillator frequency. The resonant cavities in FIG. 5 are not limited to the parallel connection, and the resonant cavities can also be formed in series. The starting oscillation condition at this time is Rr<|-R|. A common way to directly adjust the frequency is to use a varactor diode to change the capacitance Cr to adjust the frequency. However, using a varactor diode to modulate the FSK signal, its frequency hopping amplitude Δf is often greatly limited by the change of the variable capacitance value of the varactor diode, because fo is inversely proportional to √(LrCr), and Cr is a resonant cavity equivalent capacitance value. Since the resonant frequency is inversely proportional to the square root of the equivalent capacitance value Cr, a large capacitance change is required to perform a large frequency hopping action and complete the frequency hopping function of the M-element FSK. The second disadvantage is that varactor diodes with large variations not only require different bias voltages (usually much higher than that of the oscillator), but also are expensive and difficult to realize circuit integration. In addition, the varactor diode has a low Q value in the integrated circuit, so the loss is relatively large. An IC circuit for M-ary FSK is disclosed in US Patent 6,078,226 entitled "Integrated Circuit Implementation of FSK Oscillator", as shown in FIG. 6 . The circuit uses the power supply to switch the FSK oscillator, and uses the switch to change the reactance value of the SAW resonator to achieve high-speed switching action. However, this circuit shares a SAW resonator, and a combination of different switches is used to change the reactance value to realize the action of M element FSK. However, the modulation range of this method has been greatly limited by the SAW resonator, so the frequency hopping distance (Δf) cannot be too large, which limits the data rate.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a high-speed power-saving coded M-element FSK modulator.

The present invention provides a kind of high-speed power-saving coded M-element FSK modulator, wherein M is the number of frequencies to be jumped by the frequency shift key modulator, and the FSK modulator includes a coding unit, which can be obtained according to (N-1 ) bit control signal produces M/2 Gray code signals, and also receives an enable signal, and the encoding unit outputs a 0 signal when the enable signal is not in action, wherein M=2 ^N , N is a positive integer, and M is a positive an even number; and M/2 switching oscillator circuits. And each switching oscillation circuit comprises a composite quartz resonator with a first end and a second end respectively; a first switch controlled by a Gray code signal, one end of which is connected to the first end of the composite quartz resonator, and the other One end is grounded through an equivalent negative resistance circuit; a second switch is controlled by a serial data, one end of which is connected to the second end of the composite quartz resonator, and the other end is grounded; and a capacitor, one end of which is connected to the composite quartz the second end of the resonator, while the other end is grounded.

The control signal is used to control the operation of one of the M/2 switch-type oscillating circuits, and the frequency of the operating oscillating circuit is jumped by the serial data, so as to realize the frequency hopping of M elements.

Description of drawings

Fig. 1 is the block circuit diagram of the M-element FSK modulator of high-speed power-saving coding of the present invention;

Fig. 2 is an example of the circuit diagram of the switch mode oscillation circuit of Fig. 1;

FIG. 3 is a relation diagram between an enabling signal and an oscillating signal;

Figure 4 shows several typical schemes of composite quartz resonators;

Figure 5 is a simplified circuit of a known oscillator; and

FIG. 6 is an example of an integrated circuit implementation of a known M-ary FSK oscillator.

Detailed ways

FIG. 1 is a system block diagram of a high-speed power-saving coded M-element FSK modulator 100 of the present invention. The modulator 100 includes an encoding unit 200 and M/2 switching oscillation circuits 700 . The encoding unit 200 receives N−1 encoded signals, and outputs a so-called Gray code (Graycode) 210 of M/2 bits. The switch oscillator circuit 700 receives the serial data 220 (Serial Data) and the Gray code 210 of the encoding unit 200 . In this embodiment, M is the hopping frequency of the FSK modulator 100, and M=2 ^N , where N is a positive integer.

As shown in FIG. 1, the switch type oscillation circuit 700 includes a composite quartz resonator 400, a first switch 500 for controlling the action of the resonator 400, a second switch 300 for controlling the resonant frequency of the resonator 400, and adjusting the resonator 400. The resonant frequency capacitor 310 and the equivalent negative resistance circuit 600 connected to the first switch 500 . Therefore, the first switch 500 of each switch-type oscillating circuit 700 is connected to the one-bit Gray code 210, and the Gray code 210 controls whether to operate or not. Since only one bit of the output of the Gray code 210 is 1, only one of the M/2 switching oscillation circuits 700 can be activated at the same time. Furthermore, the second switch 300 is controlled by the serial data 220 . The serial data 220 is a series of 0 and 1 signals, so that the second switch 300 is turned on and off according to the serial data 220 . Therefore, the series capacitance of the composite quartz resonator 400 will change as the second switch 300 is turned on and off, thereby changing the resonant frequency of the composite quartz resonator 400 . Since each switch-type oscillating circuit 700 can provide two different resonant frequencies, the M/2 switch-type resonant oscillating circuits 700 can provide M frequencies in total.

In addition to the serial data 220 and N−1 encoding signals, the encoding unit 220 also has an enable signal input. When the enable signal is "1" (logic high), the encoding unit 200 normally generates the Gray code 210 to control M frequency hopping signals; when the enable signal is "0" (logic low), the encoding unit 200 outputs all Set to "0", therefore, all switching oscillator circuits 700 are in a dormant state. When wireless transmission is not required, the enable signal can be set to "0". At this point, the M-ary FSK is in a dormant state and does not consume any energy.

When it is desired to generate eight frequency combinations, it is necessary to set M=8, at this time N=2, the encoding unit 200 has two input control signals, and there are four combinations to control the four switching oscillation circuits 700 . Due to the output of the Gray code 210, only one switching oscillation circuit 700 is active at the same time, and the rest are in the off state. Each switching oscillation circuit is controlled by the serial data 220 to generate two frequencies, so there are eight frequency combinations in total.

The switching oscillator circuit 700 shown in FIG. 1 can be implemented by a hybrid or integrated circuit of CMOS (Complementary Metal Oxide Semiconductor) and bipolar transistors. FIG. 2 shows a circuit diagram of an embodiment of a switched oscillator circuit 700 . The oscillating circuit 700 only uses two transistors for signal switching with extremely low power loss and the operation principle of oscillator switching.

As shown in FIG. 2 , the switched oscillator circuit 700 uses a transistor 303 to play the role of the switch 300 in FIG. 1 . When the serial data 220 is "0" (ground voltage or lower than NMOS Vth), the transistor 303 cannot be forward biased, so a very high voltage is formed between the collector and emitter (drain and source) of the transistor 303 Impedance, that is, the open circuit state. Therefore, one end of the composite quartz resonator 401 is grounded through the series capacitor 402 to form a first resonant frequency.

And when the serial data 220 is "1" (generally 3V voltage), this signal is connected to the base of the transistor 303 (or the gate of the NMOS) through the low-pass filter formed by the resistor 301 and the capacitor 302, so as to conduct The collector and emitter of transistor 303 (or the drain and source of NMOS). And because the composite resonator adopts quartz crystal, it cannot conduct DC current, and can only allow a very small AC current to pass through. Therefore, as long as the transistor 303 has a very small base current, the transistor 303 can enter the saturation region. If the transistor 303 is an NMOS, the high voltage of the digital "1" greater than Vth is enough to make the NMOS enter the conduction state. At this time, the transistor 303 enters the conduction state without consuming any energy, and its collector to emitter (drain to source of NMOS) is usually only 2 to 3Ω or less. Therefore, the left end of the composite quartz resonator 401 only sees an almost short-circuit impedance, and the capacitor 402 is short-circuited. Therefore, one end of the composite quartz resonator 401 is directly grounded to form a second resonance frequency.

That is to say, the colpitz oscillator formed by the composite quartz resonator 401 , transistor 603 , capacitors 601 , 602 , and resistors 604 , 501 will have two different frequencies of the oscillator determined by the level of the serial data. That is, a first resonant frequency formed by the composite quartz resonator 401 connected in series with the capacitor 402 and another resonant frequency defined by the composite quartz resonator 401 .

Furthermore, the transistor 603 in FIG. 2 is not only used as an oscillator, but also as a switch. When the gray code 210 of the encoding unit 200 is connected to the left end of the resistor 501 and the digital signal is “1”, usually about 3V, the transistor 603 is properly biased, and its bias operating point is determined by the resistor 501 and the resistor 605 . At this time, the transistor 603 is used as an oscillator, and the oscillation signal is output through the capacitor 605 . If the signal of the Gray code 210 is "0", there is no forward bias voltage between the base and emitter of the transistor 603, so the transistor 603 is in a non-conductive state, so that a very high voltage is formed between the collector and the emitter of the transistor 603. The impedance is similar to the open circuit state of the switch circuit. At this point the oscillator is disabled, resting and consuming little power. The conduction or non-conduction of the transistor 603 can be controlled only by the very small base current of the transistor 603 passing through the resistor 501 . Therefore, its switching action is quite fast.

With the help of sophisticated simulation technology, using Agilent ADS software and the sophisticated model of its transistor (NPN_2N2222A) database, Figure 3 shows that when the enable signal jumps from 0 to 3V, and its rise time and fall time are both 10μsec, the serial The data 220 is 5 kbps. The oscillator formed by the transistor 603 in FIG. 2 has an analog data of start-up oscillation time and shut-down oscillation time of about 5 μsec, which is shorter than the rise time and fall time of the digital signal. Therefore, the time to start and stop the oscillator is determined by the rise time and fall time of the enable signal, which is much faster than circuits such as PLL.

FIG. 4 shows several typical designs of the composite quartz resonator 401 in FIG. 2 . This composite quartz resonator 401 is based on a quartz resonator (Figure 4(a)), and can be connected in series with a single inductor (Figure 4(b)) or in series with a single capacitor (Figure 4(c)) or in series with an inductor and a capacitor (Figure 4(d)) to change the FSK signal modulation depth.

The invention proposes a high-efficiency (power-saving) high data rate M-FSK frequency hopping design. This new design allows the transistor to perform two actions of the oscillator and high-speed switching at the same time, and the switch oscillator is placed in a coded circuit structure (the coder can use a Gray code coder, using the Gray code to only Change the characteristics of one bit to start a group of external composite crystal oscillators (Composite Crystal Oscillator) at high speed each time to form an M-element FSK modulator composed entirely of transistors, which is suitable for circuit integration. It is especially suitable for radio digital transmission systems that have special requirements for power saving. Examples include satellite communications or high-efficiency wireless communication devices that require batteries.

Although the structure of the instantaneous analog-to-digital converter of the present invention is described above with a preferred embodiment, it does not limit the scope of the present invention. As long as it does not depart from the spirit of the present invention, those of ordinary skill in the art can make various modifications or changes. .

Claims (5)

1. A high-speed power-saving coded M-element frequency-shift key modulator, wherein M is the number of frequencies to be jumped by the frequency-shift key modulator, and the frequency-shift key modulator includes: An encoding unit can generate M/2 Gray code signals according to the N-1 bit control signal, and also receive an enabling signal, and the encoding unit outputs a 0 signal when the enabling signal is inactive, wherein M=2 ^N , N is a positive integer and M is a positive even number; and M/2 switching oscillating circuits, including: A composite quartz resonator with a first end and a second end; A first switch, controlled by the gray code signal, and one end is connected to the first end of the composite quartz resonator, and the other end is grounded through an equivalent negative resistance circuit; A second switch, controlled by a serial data, one end is connected to the second end of the composite quartz resonator, and the other end is grounded; and a capacitor with one end connected to the second end of the composite quartz resonator and the other end connected to ground; Using the control signal to control the operation of one of the M/2 switch-type oscillation circuits, and jumping the frequency of the operating oscillation circuit by the serial data, so as to realize the frequency jumping of M elements. 2. The high-speed power-saving coded FSM-ary frequency shift key modulator according to claim 1, wherein said switch-type oscillating circuit outputs an oscillating signal via said first switch. 3. The high-speed power-saving coded M-element frequency shift key modulator according to claim 1, wherein said composite quartz resonator is a quartz crystal connected in series with a capacitor. 4. The high-speed power-saving coded M-element frequency-shift key modulator according to claim 1, wherein said composite quartz resonator is a quartz crystal connected in series with an inductor. 5. The high-speed power-saving coded M-element frequency shift key modulator according to claim 1, wherein said composite quartz resonator is a quartz crystal connected in series with a capacitor and an inductor.

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