37results about How to "Wide output frequency range" patented technology

The object of the invention is to obtain a stable, locked clock with reduced output jitter in a digital phase-locked loop circuit. Control oscillating part 12 has frequency divider 18, period measurement circuit 20, moving average value computation circuit 22, and output clock generator 24. In intermediate oscillating frequency divider 18, as a result of tracking to synchronization control signals c, d from phase comparator 10, there is a wide variation in the period of intermediate clock g. However, by means of period measurement circuit 20 and moving average value computation circuit 22, varying slowly with a small fluctuation amplitude, period i of the moving average is obtained, and a stable output clock j that tracks reference clock a slowly and reliably is obtained from output clock generator 24.

The invention discloses a phase-locked loop frequency synthesizer which is characterized in that the phase-locked loop frequency synthesizer comprises a phase-frequency phase discriminator, a charge pump, a low-pass filter, a broadband differential LC oscillator provided with a capacitor array of a control switch, a multimode frequency divider and a controller which is used for a self-adapting frequency regulating curve; the analogue signal control end of the broadband differential LC oscillator is connected with an output signal Vctrl of the low-pass filter, and the digital signal control end thereof is connected with the output end of the controller. The phase-locked loop frequency synthesizer further comprises a 3-order full digital Sigma-delta modulator provided with a three-bit quantizer. The phase-locked loop frequency synthesizer can realize fractional frequency division, and the output frequency signals thereof can be continuously changed at a wide range, and the precision of the frequency spectrum is high.

A first exemplary aspect of an embodiment of the present invention is a phase-locked loop circuit including: a voltage-current converter that converts a control voltage into a control current, the control voltage generated according to a phase difference between an input pulse signal and a feedback pulse signal fed back from an output side of a current controlled oscillator; the current controlled oscillator that generates an output pulse signal having a frequency according to the control current; a current detection unit that detects the control current; and a frequency range switch that switches a frequency range of the output pulse signal according to the detected control current.

The invention provides a built-in oscillation circuit. A negative feedback closed loop circuit type is adopted for the built-in oscillation circuit, and a frequency-voltage conversion mode is used for the built-in oscillation circuit, and therefore the built-in oscillation circuit is enabled to be completely integrated in a chip, crystal oscillators needing to be additionally arranged are saved, and process cost is saved. An oscillation frequency generated by an annular oscillator is converted into a feedback voltage and compared with a reference voltage, then compared results are fed back to a control end of the annular oscillator, the frequency of the annular oscillator is changed, the output frequency deviation is compensated, and therefore work frequency with low temperature drift is output by a loop circuit, and output frequency with high precision is generated.

The present invention provides a low phase noise wideband microwave local oscillator source circuit which is formed by two phase-locked loops. The frequency division signal of a broadband voltage-controlled oscillator directly enters a phase detector to form phase-locked loops with a reference signal, and the preset of the whole loop is realized. Then through switch switching, the output signal of the voltage-controlled oscillator and the frequency doubling and frequency division of a sampling ring output signal are mixed, the phase locking is carried out again, and the function of a low noise is realized. According to the low phase noise wideband microwave local oscillator source circuit, a wideband VCO chip is used, the outputted frequency range is 3GHz to 10GHz, and the phase noise of a 10GHz signal can reach -120dBc / Hz@10kHz. According to the low phase noise wideband microwave local oscillator source circuit, while very low phase noise is obtained, the number of used devices is greatly reduced, a PCB space is saved, the volume is only 16cm by 9cm by 2cm, the debugging difficulty is reduced, and the power consumption is reduced.

The invention discloses a frequency characteristic detecting system of an electronic type voltage transformer. The frequency characteristic detecting system comprises a frequency conversion power supply, a boosting unit, a high frequency voltage divider, a merging unit and a frequency characteristic detecting unit. The nominal voltage of the output end of the frequency conversion power supply adjusts the voltage amplitude of a power supply through the boosting unit to supply the primary side high voltage U1 used in an experiment to the electronic type voltage transformer to be detected; the primary side high voltage U1 is converted into the low voltage U2 through the high frequency voltage divider, and the low voltage U2 is used as standard source signals of the frequency characteristic detecting unit; the sampling value of the electronic type voltage transformer to be detected is sent to the frequency characteristic detecting unit through the merging unit, and the sampling value is used as detected signals of the frequency characteristic detecting unit. The frequency characteristic detecting system of the electronic type voltage transformer can reliably and perfectly detect the frequency characteristics of the electronic type voltage transformer, and aims to improve the frequency transmission performance of the electronic type voltage transformer and provide the technical guarantee for safe and stable operation of the electronic type voltage transformer.

The invention discloses a FPGA-based digital radio frequency transmitter. The digital radio frequency transmitter comprises a frequency conversion and coding module, a radio frequency digital-to-analog conversion module, a combining and filtering module and an electrically tunable filtering module. The main working process of the FPGA-based digital radio frequency transmitter is as follows: a digital baseband signal is subjected to frequency conversion and coding processing of the LUT mapping module to obtain a 1-bit digital signal of a specific frequency band, the 1-bit digital signal is converted into an analog radio frequency signal through the radio frequency digital-to-analog conversion module, and noise components in the analog radio frequency signal are filtered out through the combining filtering module and the electrically tunable filtering module. According to the invention, except the combination filtering module and the electrically tunable filtering module, other processing modules are FPGA-based digital modules; signals with specific frequency and bandwidth can be defined, the frequency modulation range is wide, the integration level is high, and the requirements of modern wireless communication transmitters are met.

The invention introduces a UHV (Ultra High Voltage) transformer field variable frequency partial discharge test device. A No.1 frequency conversion cabinet (2) and a No.2 frequency conversion cabinet (3) are connected in parallel between a control cabinet (1) and an exciting transformer (4) of the UHV transformer field variable frequency partial discharge test device; the high voltage output end of the exciting transformer (4) is connected in parallel with a capacitive voltage divider (5), a compensation reactor (6) and a 1,000kV AC (Alternate Current) UHV transformer (7); and the 1,000kV AC UHV transformer (7) is connected in parallel with a partial discharge tester (8) by end screens of high voltage, intermediate voltage and low voltage sleeves of the 1,000kV AC UHV transformer (7). The device has the advantages that 1, adaptability is strong; 2, the device has a small volume and a light weight and is convenient to transport and assemble; 3, reliability is high and the voltage and the frequency can be continuously regulated; 4, direct contact between people and live equipment is avoided and safety is high; and 5, the device has a wide output frequency range and also can be used as a withstand voltage test variable frequency power supply of equipment such as a UHV GIS (Gas Insulated Switchgear), a mutual inductor and the like.

A first exemplary aspect of an embodiment of the present invention is a phase-locked loop circuit including: a voltage-current converter that converts a control voltage into a control current, the control voltage generated according to a phase difference between an input pulse signal and a feedback pulse signal fed back from an output side of a current controlled oscillator; the current controlled oscillator that generates an output pulse signal having a frequency according to the control current; a current detection unit that detects the control current; and a frequency range switch that switches a frequency range of the output pulse signal according to the detected control current.

The invention discloses a broad-band radio-frequency generation circuit based on a VC-TCXO (Voltage Control-Temperature Compensation Crystal Oscillator) array and a frequency synthesizing chip, which comprises a VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array, a frequency synthesizing chip, a modulator, a direct digital frequency synthesizer, a power controller and adigital processor; the digital processor is connected with the control end of the VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array, the control end of the frequency synthesizing chip, the control end of the power controller and the input end of the direct digital frequency synthesizer separately; the output end of the VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array is connected with the reference input end of the frequency synthesizing chip; the output end of the frequency synthesizing chip is connected with the carrier input end of the modulator; the I / Q baseband output end of the direct digital frequency synthesizer is connected with the I / Q baseband input end of the modulator; and the output end of the modulator is connected with the signal input end of the power controller. The broad-band radio-frequency generation circuit has the advantages of wide output frequency range, high frequency resolution, low noise coefficient, good stray performance and the like.

The invention discloses a three-level and five-level hybrid modulation method for a single-phase inverter, and the method comprises the steps: employing an inverter circuit which comprises a DC powersupply, a field effect transistor, an inductor, a capacitor and a resistor, and enabling an AC side midpoint to be connected with a DC side midpoint N through the inverter circuit in order to reduce acommon-mode voltage; and according to the method, a three-level modulation method and a five-level modulation method are used in a mixed mode, the three-level modulation method is used when the modulation ratio is higher than 0.2, the five-level modulation method is used when the modulation ratio is lower than 0.2, and the method has the following remarkable advantages that the output voltage range is 2-115 V, the output frequency range is 47-10000 Hz; THD can meet the requirement that THD is smaller than 2% through mixed use of the three-level modulation and five-level modulation methods; the circuit is compact in structure and small in size; and the output power is high and can reach 6VA.

The invention discloses a programmable capacitor array-based frequency band phase-locked loop, which is characterized in that a phase frequency detector circuit is sequentially connected with a charge pump circuit, a switch loop filter and a multiband voltage-controlled oscillator circuit, and the multiband voltage-controlled oscillator circuit is connected with the phase frequency detector circuit through a programmable frequency divider circuit; the phase frequency detector circuit is connected with the switch loop filter through the switch control circuit; reference clock signals clkref and clkdiv generate control signals UP and DN through the phase frequency detector, the charge pump converts a received pulse difference signal into a current signal, then the current signal is converted into a voltage signal through the loop filter to be used for controlling the frequency change of the voltage-controlled oscillator, discrete frequency modulation is achieved by changing the load capacitance, and the frequency of the voltage-controlled oscillator is adjusted. A programmable capacitor array structure is utilized to obtain a frequency output range, and output is fed back to a phase frequency detector through a frequency divider to realize loop locking. Under the condition that the gain of the voltage-controlled oscillator is reduced, low phase noise of the voltage-controlled oscillator is achieved, and meanwhile a wide output frequency range is obtained.

An off-chip adjustable relaxation type voltage-controlled oscillator circuit belongs to the technical field of power electronics. The circuit comprises a current generation unit, a spike absorption unit, an oscillation and compensation unit and an output buffer unit, wherein the current generated by the current generation unit is used to charge and discharge a capacitor in the oscillation and compensation unit, and the current can be controlled by an off-chip adjustable voltage that is given in an off-chip mode; the oscillation and compensation unit is used to generate an oscillation signal according to the charge and discharge of the capacitor, controls the frequency of the oscillation signal by using the current generated by the current generation unit, and can improve the adjustabilityof the oscillation frequency of the oscillation signal through compensation; the spike absorption unit is used to eliminate voltage spikes generated by parasitic capacitance when the charge and discharge states are switched, and can improve the noise suppression capability; and the output buffer unit is mainly used to shape the output oscillation signal, can remove the glitch of the output signal,and ensures that the output oscillation signal is more ideal.

A differential signal driven direct-current voltage generating device is proposed, which is designed for use with a PLL (phase-locked loop) circuit or a DLL (delay-locked loop) circuit system for generating an output of a direct-current (DC) voltage in response to a pair of differential signals, such as phase-difference signals; and which is characterized by the utilization of a capacitor-switched voltage doubler for doubling the output voltage of a charge pump so that the doubled voltage can be used as a control voltage for a PLL-VCO (voltage-controlled oscillation) or a DLL-VCDL (voltage-controlled delay line) circuit for generation of an output oscillating signal with a wider frequency range.

The invention relates to a low-power voltage-frequency adjustable inverted sine wave signal source, which is mainly composed of a signal source controller, an inverting circuit, a digital power amplification circuit, an overcurrent protection circuit, a voltage feedback circuit and a DC power supply, wherein the inverting circuit adopts a 12-bit serial DA converter, and the DA converter receives aserial control signal sent by the signal source controller and generates a controllable DC voltage signal with corresponding amplitude; the DC voltage signal is connected to an analog switch, and a control end of the switch is controlled by a frequency control square-wave signal generated by the signal source controller and outputs a square-wave voltage signal with the same frequency as the control signal and controllable voltage amplitude. The low-power voltage-frequency adjustable inverted sine wave signal source has the remarkable advantages that the output voltage is wide in range and canbe adjusted within 2-115V; the output frequency is wide in range and can be adjusted within 360-10000Hz; the output voltage adopts closed-loop control, and the precision can reach up to 2% under an on-load condition; the circuit devices are compact, and the size is small; and the output power is high and can reach up to 5W.

The invention discloses a high-precision wide-range relaxation oscillator which is insensitive to temperature, including a bias voltage (101), a reference current (102), a programmable current mirror (103), a relaxation oscillator unit (104) and a shaping Logic (105) module; provide programmable charge and discharge current for the relaxation oscillator unit through bias voltage (101), reference current (102) and programmable current mirror (103), so as to realize wide-range frequency characteristics of multi-band output; through The frequency adjustment and temperature compensation technology in the reference current (102) realizes the coarse adjustment and fine adjustment of the output frequency of each frequency band, and produces a high-precision output clock; at the same time, it uses the positive temperature coefficient characteristics of the resistance and the negative temperature coefficient characteristics of the triode to achieve full temperature Within the range, the output frequency of the oscillator is insensitive to temperature and has good temperature drift characteristics; the shaping logic (105) compares the output waveform of the relaxation oscillator unit, multiplies the frequency, and feedbacks the charging and discharging of the capacitor, and finally outputs a clock signal of the target frequency. The relaxation oscillator proposed in this patent has the characteristics of wide output frequency range, high precision and insensitivity to temperature.

The invention discloses a nanosecond level narrow pulse signal generating circuit capable of implementing continuous frequency modulation. The nanosecond level narrow pulse signal generating circuit comprises an adjustable square wave generating circuit and a digital logic processing circuit. The adjustable square wave generating circuit comprises an NE555 chip, a first adjustable resistor module,a second adjustable resistor module, a first capacitor and a second capacitor, and is used for obtaining a square wave signal. After the narrow pulse signal generating circuit is established, the frequency of the output pulse can be changed by adjusting the resistance of any one of the resistor modules. The digital logic processing circuit comprises a 74HC04 chip, a 74HC86 chip, a 74HC08 chip anda third capacitor, and is used for performing a logic operation on the obtained square wave signal to obtain a nanosecond level narrow pulse. The nanosecond level narrow pulse signal generating circuit disclosed by the invention obtains the nanosecond level narrow pulse, satisfies the requirements that the pulse output frequency is continuously adjustable, and provides a basis for the ultra-wideband (Ultra-Wide Band, UWB) wireless communication technology.

The invention provides a voltage-current converting circuit, belonging to the field of voltage-current conversion. The voltage-current converting circuit comprises a first MOS (metal oxide semiconductor) pipe, a second MOS pipe, a first current lens, a second current lens and a load; the first MOS pipe and the first current lens are formed into a first level voltage-current converting circuit; the second MOS pipe and the second current lens are formed into a second level voltage-current converting circuit; the grid of the first MOS pipe is connected with the input voltage, the source electrode of the first MOS pipe is earthed, the drain electrode of the first MOS pipe is connected with the source electrode of the second MOS pipe and the first current lens, and the first current lens is connected with the load; the grid of the second MOS pipe is connected with the input voltage and is connected with the grid of the first MOS pipe, the drain electrode of the second MOS pipe is connected with the second current lens, and the second current lens is connected with the load; and the load is earthed. The voltage-current converting circuit provided by the invention increases the grade of the voltage-current converting circuit, and improves the linearity of the voltage-current conversion.

The invention discloses a high-precision wide-range relaxation oscillator insensitive to temperature. The relaxation oscillator comprises a bias voltage module (101), a reference current module (102),a programmable current mirror (103), a relaxation oscillator unit (104) and a shaping logic module (105). A programmable charging and discharging current is provided for the relaxation oscillator unit through a bias voltage (101), the reference current module (102) and theprogrammable current mirror (103), and the wide-range frequency characteristic of multi-band output is achieved; coarse adjustment and fine adjustment of the output frequency of each frequency band are realized through frequency adjustment and temperature compensation technologies in the reference current (102), and a high-precision output clock is generated; meanwhile, the positive temperature coefficient characteristic of the resistor and the negative temperature coefficient characteristic of the triode are utilized toachieve the good temperature drift characteristic that the output frequency of the oscillator is insensitive to the temperature in a full temperature range; and the shaping logic module (105) performs comparison, frequency multiplication and feedback control of charging and discharging of a capacitor on the output waveform of the relaxation oscillator unit, and finally outputs a clock signal witha target frequency. The relaxation oscillator provided by the utility model has the characteristics of the wide output frequency range, high precision and insensitivity to temperature.

Provided is a configurable voltage-controlled oscillator applied to an FPGA. A ring oscillator serves as a core part of the voltage-controlled oscillator and is provided with extra digital control signals used for controlling frequency of an oscillation center. The control signals are configured by means of configuration information of the FPGA, center frequency of the voltage-controlled oscillator can be adjusted, and therefore output frequency of the voltage-controlled oscillator can be continuously adjusted within a large range.

A three-level and five-level hybrid modulation method for a single-phase inverter, the method uses an inverter circuit including a DC power supply, a field effect transistor, an inductor, a capacitor, and a resistor, and the inverter circuit is used to reduce the common-mode voltage , connect the midpoint of the AC side to the midpoint N of the DC side; this method mixes the three-level and five-level modulation methods, and uses the three-level modulation method when the modulation ratio is higher than 0.2, and uses the three-level modulation method when the modulation ratio is lower than 0.2 When using the five-level modulation method, it has the following significant advantages: the output voltage range is 2~115V; the output frequency range is 47~10000Hz; through the mixed use of three-level modulation and five-level modulation methods, the THD can reach the requirement of less than 2%. ; Circuit structure is compact, small size; high output power, up to 6VA.

The present invention proposes a low-phase-noise wide-band microwave local oscillator source circuit, which is composed of two phase-locked loops. The frequency-division signal of the broadband voltage-controlled oscillator directly enters the phase detector and the reference signal to form a phase-locked loop, realizing the whole The preset setting of the loop; then through the switch, the output signal of the voltage controlled oscillator is mixed with the frequency multiplication and frequency division of the output signal of the sampling loop, and the phase locking is performed again to realize the low noise function. The low phase noise broadband microwave local oscillator source circuit of the present invention adopts a broadband VCO chip, and the output frequency range is 3GHz‑‑‑10GHz, and the phase noise of the 10GHz signal can reach ‑120dBc / Hz@10kHz; the present invention obtains While the phase noise is extremely low, the number of components used is greatly reduced, and PCB space is saved. The volume is only 16cm×9cm×2cm, which reduces the difficulty of debugging and reduces power consumption.

The invention relates to an external RC frequency adjustable oscillator in oscillators. The external RC frequency adjustable oscillator comprises a reference voltage generation circuit 1, a charging circuit 2, a discharge circuit3, and a clock processing circuit 4; the reference voltage generation circuit 1 is used for generating and outputting a reference voltage signal, and the discharge circuit3 is used for discharging charges on the capacitor C2; the discharging circuit 3 comprises a comparator, the charging circuit 2 comprises a capacitor C2, and the voltage on the capacitor C2 is directly fed back to the positive input end of the comparator; and the clock processing circuit 4 is used for enhancing driving and shaping of output. The oscillator is wide in output frequency range, simple in structure, small in area and convenient and flexible to use, and can be widely applied to MCU and other electronic products needing clocks.

Provided is a configurable voltage-controlled oscillator applied to an FPGA. A ring oscillator serves as a core part of the voltage-controlled oscillator and is provided with extra digital control signals used for controlling frequency of an oscillation center. The control signals are configured by means of configuration information of the FPGA, center frequency of the voltage-controlled oscillator can be adjusted, and therefore output frequency of the voltage-controlled oscillator can be continuously adjusted within a large range.

The invention is a low-power voltage-frequency adjustable inverter sinusoidal signal source, which is mainly composed of a signal source controller, an inverter circuit, a digital power amplifier circuit, an overcurrent protection circuit, a voltage feedback circuit and a DC power supply; the inverter circuit adopts 12-bit serial DA converter, the DA converter receives the serial control signal sent by the signal source controller, and generates a controllable DC voltage signal of corresponding amplitude; the DC voltage signal is connected to the analog switch, and the control terminal of the switch is controlled by the signal source The controller generates a frequency-controlled square-wave signal for control, and outputs a square-wave voltage signal with the same frequency as the control signal and a controllable voltage amplitude. The invention has the following remarkable advantages: wide output voltage range, adjustable from 2 to 115V; wide output frequency range, adjustable from 360 to 10000Hz; closed-loop control for output voltage, which can reach 2% accuracy under load conditions; compact circuit devices, Small size; high output power, up to 5W.

The invention provides a voltage-current converting circuit, belonging to the field of voltage-current conversion. The voltage-current converting circuit comprises a first MOS (metal oxide semiconductor) pipe, a second MOS pipe, a first current lens, a second current lens and a load; the first MOS pipe and the first current lens are formed into a first level voltage-current converting circuit; the second MOS pipe and the second current lens are formed into a second level voltage-current converting circuit; the grid of the first MOS pipe is connected with the input voltage, the source electrode of the first MOS pipe is earthed, the drain electrode of the first MOS pipe is connected with the source electrode of the second MOS pipe and the first current lens, and the first current lens is connected with the load; the grid of the second MOS pipe is connected with the input voltage and is connected with the grid of the first MOS pipe, the drain electrode of the second MOS pipe is connected with the second current lens, and the second current lens is connected with the load; and the load is earthed. The voltage-current converting circuit provided by the invention increases the grade of the voltage-current converting circuit, and improves the linearity of the voltage-current conversion.

The invention provides a feedback regulating oscillator, which belongs to the technical field of integrated circuits. The oscillator includes: a current source circuit for outputting three bias currents; a charging and discharging circuit for charging and discharging according to the first bias current, converting a correspondingly generated frequency signal into a voltage signal and output; an operational amplifier circuit, configured to start working in response to the second bias current, to amplify and output the voltage signal; a current-controlled oscillator, configured to amplify the voltage signal according to the third bias current, The amplified voltage signal is converted into a current signal, and then the current signal is converted into a clock signal in the form of frequency and output; and a digital logic circuit is used to convert the clock signal into a clock control signal and output and control the clock The signal is fed back to the charging and discharging circuit and the current source circuit. The present invention can meet the requirements of any one or more of low voltage, low power consumption, and high precision characteristics.

An off-chip adjustable relaxation voltage-controlled oscillator circuit belongs to the technical field of power electronics. It includes a current generation unit, a peak absorption unit, an oscillation and compensation unit and an output buffer unit. The current generated by the current generation unit is used to charge and discharge the capacitance in the oscillation and compensation unit, and the current can be given by off-chip. Adjust the voltage to control; the oscillation and compensation unit is used to generate the oscillation signal according to the charge and discharge of the capacitor, and use the current generated by the current generation unit to control the frequency of the oscillation signal, and can improve the adjustability of the oscillation frequency of the oscillation signal through compensation; spike The absorption unit is used to eliminate the voltage spikes caused by parasitic capacitance when switching between charge and discharge states, and improve the noise suppression capability; the output buffer unit is mainly used for shaping the output oscillation signal, which can remove the burr of the output signal, so that the output oscillation signal more ideal.

The invention relates to a flat-plate bone conduction earphone with an adjustable sound-receiving part, which includes a main bracket, two angle adjustment structures and two sounding units based on a flat-plate vibration unit, wherein the sounding unit is connected to the main bracket through the angle adjustment structure, The cross-shaped chute on the main bracket, the connecting piece in the rotating groove and the angle adjustment structure, and the elastic bracket realize the diverse adjustment of the position of the sound unit. Fit the position to avoid head hair, ornaments or glasses brackets from interfering with the wearing and sound collection of bone conduction headphones, and improve the listening effect of bone conduction headphones.

The invention discloses a broad-band radio-frequency generation circuit based on a VC-TCXO (Voltage Control-Temperature Compensation Crystal Oscillator) array and a frequency synthesizing chip, which comprises a VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array, a frequency synthesizing chip, a modulator, a direct digital frequency synthesizer, a power controller and a digital processor; the digital processor is connected with the control end of the VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array, the control end of the frequency synthesizing chip, the control end of the power controller and the input end of the direct digital frequency synthesizer separately; the output end of the VC-TCXO (Voltage Control - Temperature Compensation Crystal Oscillator) array is connected with the reference input end of the frequency synthesizing chip; the output end of the frequency synthesizing chip is connected with the carrier input end of the modulator; the I / Q baseband output end of the direct digital frequency synthesizer is connected with the I / Q baseband input end of the modulator; and the output end of the modulator is connected with the signal input end of the power controller. The broad-band radio-frequency generation circuit has the advantages of wide output frequency range, high frequency resolution, low noise coefficient, good stray performance and the like.