Abstract: Because the general purpose oscilloscope has not saved the function, thus receives the enormous limit in the single signal impulse’s capture and the survey. Introduced that one kind gives the general purpose oscilloscope inserting memory function using the SPCE061A 16 monolithic integrated circuits the principle. The experiment proved that this design in certain frequency range is feasible, moreover the cost is low, has certain use value.
Key word: Oscilloscope; SPCE061A; Monolithic integrated circuit; Memory; Design
Chinese Library classification number: TM935.3 document code: A article serial number: 1006-6977 (2006) 01-0051-03
1 introduction
At present, general two trace oscilloscope like HH4310A/HH4311A, RS8 and so on do not have the memory function, in the student tests can satisfy the signal measurement the request, but if uses in surveying some non-week promissory note signal impulse, as a result of the signal burst characteristics, these general oscilloscopes often cannot to the signal profile, the peak-to-peak value, the pulse width carry on the careful observation. It inserts the memory function in the general purpose oscilloscope, can expand the application scope enormously, has the high use value. The author introduced that one kind uses the SPCE061A 16 monolithic integrated circuits to insert the memory function in the HH4310A/HH4311A general purpose oscilloscope the principle and the experimental result.
2 general purpose oscilloscope’s key job principles
General purpose oscilloscope’s frequency is many, the electric circuit is various, but generally speaking, may induce is 3 key components: The vertical system (mainly realizes Y input signal enlargement); The horizontal system (mainly realizes horizontal scanning and level enlargement) and the main engine (mainly includes low/high-voltage power supply and display circuit). Basic structure as shown in Figure 1, each constituent detailed principle of work reference reference [1].
3 inserting memory function principle
Inserts the memory function in the general purpose oscilloscope the basic principle is with a/D switch the simulation signal conversion for the digital signal, then saves to RAM, when needs to demonstrate, reads out the RAM in memory’s digital signal according to the order, restores the simulation signal through the D/A switch, demonstrates on the oscilloscope fluorescent screen. In the design, uses SPCE061A in 16 monolithic integrated circuit’s A/D switches to realize to oscilloscope’s Y input was measured that the signal the mold/number transforms, the transformation result saves in SPCE061A internal SRAM, when demonstrates, resumes the input after the SPCE061A D/A switch the simulation signal, the expander which SPCE061A and the related electric circuit constitute meets between the general purpose oscilloscope vertical system’s Y input circuit and the Pre-amplifier, as shown in Figure 2.
3.1 A/D transforms principle and performance requirement
Must realize to inputs was measured that the signal the memory, A/D transforms (sample, quantification, code) is a key, according to Naikuisite (Nyquist) cardinal theorem, after Qujiang, can return to original state not distorted the original signal, must satisfy fs>2fm, namely the sampling frequency must be bigger than the signal upper frequency 2 times. Has 7 groups 10 in SPCE061A to approach a/D switch gradually, uses in common to A/D switch related control register P_ADC_Ctrl ($7015H), P_ADC_MUX_Ctrl ($702BH) the reasonable establishment starts A/D to transform, ($702CH) in the unit reads out the value which from P_ADC_MUX_Data A/D transforms. In SPCE061A A/D transforms maximum speed for (Fosc/32/16Hz), if the speed surpasses this value, from P_ADC_MUX_Data when readout will have the mistake. A/D transforms the biggest frequency corresponding rate (Fosc/32/16Hz) as shown in Table 1.
In SPCE061A, the 32768Hz real-time clock produces system clock Fosc, Fosc after the PLL doubling circuit to obtain the CPU clock again after the frequency division (CPUCLK), through to register P_System Clok ($7013H) the programming completes to system clock Fosc and the CPU clock rate definition. When default, Fosc, CPUCLK respectively are 24.576MHz and Fosc/8.
The basic principle which and SPCE061A A/D transforms according to A/D transform the characteristic, inserts the memory functional module most greatly not distorted frequency in the general purpose oscilloscope is 20kHz.
3.2 digital signal memory and D/A transformation
The result which transforms after A/D needs to save to the memory, its storage capacity for the gain profile’s sampling point number, after deposits a/D transformation directly the data gain memory cell expressed. Has 2K×10bit the SRAM memory cell in SPCE061A, the actual use’s SRAM capacity mainly the speed which and the scanning factor transforms by A/D (t/div) decided together that its relational following -like shows:
In the formula, fS is the sampling frequency which A/D transforms, N is each standard sample points. Thus it may be known, under A/D transformation speed same condition, storage capacity size decision trace time factor size. In the design, A/D transformation speed fS is 96kHz most greatly, if transforms with 1K SRAM as A/D memory, then the biggest trace time is 10ms/div. In the memory expansion module, after the monolithic integrated circuit starts a/D switch, through to P_ADC_MUX_Data ($702CH) in unit A/D transformation result comparison, when the effective transformation result appears, only then finally will preserve in SRAM, uses this method to be able to expand the trace time factor effectively, is effective regarding the single signal impulse’s capture. The ADC subprograms are as follows:
_AD
In a/D transformation, not only A/D transforms the figure and the storage capacity decide the oscilloscope vertical and the horizontal resolution, moreover, averages many times through the monolithic integrated circuit to a/D transformation result’s digital signal processing, eliminates the stochastic noise, may enable the vertical resolution to have the enhancement.
SPCE061A has provided 2 group D/A transformation channel, through (702AH) the unit programming controls D/A to register P_DAC_MUX_Ctrl to transform, transforms memory’s in digital signal according to the order into the simulation signal, adds to oscilloscope’s Y channel amplifier, on fluorescent screen regenerated signal profile.
4 oscilloscope storage module experimental study
Mainly uses regarding the oscilloscope storage module’s research to the identical signal carries on the way which the experiment compares. In reality, carries on 1 direct measurement and 1 secondary storage survey using the HH4310A/HH4311A general purpose oscilloscope to the signal, then to 2 measurement results (including profile degree of distortion, peak-to-peak value and frequency) carries on the comparison. Figure 3 (a) and (b) demonstrates separately to the single signal impulse direct demonstration profile and the memory demonstration profile.
May see through experimental result’s comparison, in certain frequency (20kHz) below, inserts SPCE061The oscilloscope storage module to be able to realize to the signal not distorted memory.< ?XML:NAMESPACE PREFIX = O />
5 concluding remark
May see through the experimental study, may realize using SPCE061A to the general purpose oscilloscope saves the function the expansion. May realize well through monolithic integrated circuit’s programming to the single pulse memory survey. Although in SPCE061A, A/D transformed the speed which and the SRAM capacity, D/A transformed has limited the stored signal frequency band scope, but, its cost was low, the performance-to-price ratio was high, has certain use value. If the expansion stored signal band width’s scope, may use the high speed A/D switch and the D/A switch as well as large capacity RAM realizes.
