Chapter 2 Theoretical framework
2.1 EVA’s measurement tools and specification
Because the project is based on EVA2’s tools and boards, including ADC, DAC, TMU, JTAG board, Power IO module, AFG, the functions of those tools should be researched and
elaborated. Besides, the ADC and DAC measurement tools are analogous and expounded in one part. Moreover, each measurement tool has its own specification which is an important
element for calibration and is required to do research.
2.1.1 ADC/DAC
ADC (digital-to-analog converter) and DAC (analog-to-digital converter) are systems which can convert a digital signal to analog signal or convert an analog signal to digital analog. ADC function board performs as input source for EVA setup. It can generate 96 channels of digital voltage ranging from 0 – 5V which can be defined by users (Zheng, 2018). And the DAC function board is to analog voltage ranging from 0 – 5V.
EVA2 utilizes AD7927 and AD5328 as the analog devices which are a combination of both analog machine and analog media that can together measure, record, reproduce, or broadcast continuous information (Wikipedia, Analog device, 2020).
Figure 2-1 EVA2’s ADC module schematics (NXP, Schematics of EVA2's ADC module, 2020)
6 AD7927 is a 12-bit, high speed, low power, 8-channel, SAR (successive approximation) ADC as shown in the Fig.2-1 (Analog Devices, AD7927 Data sheet, 2003). And, AD5328 is an octal 12-bit buffered voltage output DAC in a 16-lead TSSOP (Thin shrink small outline package) as shown in the Fig.2-2.
The ADC has two phases, the acquisition phase and the conversion phase. The ADC is comprised of control logic, SAR (Successive-approximation-register), and a capacitive DAC that are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition.
And the calibration device is required to measure these parameters when the user gives the command to test if the measure values are in their specifications. If not, the calibration device will calibrate it, or some components will be replaced. The specification of the ADC will be shown in the table 2-1 (Analog Devices, AD7927 Data sheet, 2003).
AVDD = VDRIVE = 2.7 V to 5.25 V, REFIN = 2.5 V;
Table 2-1 The specification of ADC
Parameter Min Max Unit Test Conditions/Comments Analog Input
Input Voltage Ranges
0 REFIN V RANGE bit set to 1
0 2 × REFIN V RANGE bit set to 0, AVDD / VDRIVE = 4.75 V to 5.25 V
Figure 2-2 EVA2’s DAC module schematics (NXP, Schematic of EVA2's DAC module, 2020)
7 For the DAC, the architecture of one DAC channel consists of a resistor string DAC followed by an output buffer amplifier. The voltage at the VREF pin provides the reference voltage for the corresponding DAC. Fig. 2-3 shows a block diagram of the DAC architecture (Analog Devices, AD5308/AD5318/AD5328 Data sheet, 2002).
(Analog Devices, AD5308/AD5318/AD5328 Data sheet, 2002) The specification of the DAC will be shown in the table 2-2.
VDD = 2.5 V to 5.5 V; VREF = 2 V; RL = 2 kΩ to GND; CL = 200 pF to GND;
Temperature range (A, B version): −40°C to +125°C; typical at 25°C.
Table 2-2 The specification of DAC (Analog Devices, AD5308/AD5318/AD5328 Data sheet, 2002) Parameters A Version
MIN Typ Max
B Version
MIN Typ Max
Unit Conditions/Comments
DAC Reference Input VREF Input
Range
1.0 VDD 1.0 VDD V Buffered reference mode
0.25 VDD 0.25 VDD V Unbuffered reference
mode
2.1.2 TMU/Oscilloscope
TMU (Time Measurement Unit) is an EVA application that can measure the time difference between two signals or between two transients of one signal (Zwam, 2017). But for the EVA2, NXP has utilized two oscilloscopes called PicoScope 2406B and PicoScope 5444D, to measure the time and to get rid of the TMU device. The specifications of the PicoScope 2406B and the PicoScope 5444D will be shown in the Table.2-3 and 2-4.
Table 2-3 The specifications of PicoScope 2406B (Pico®Technology, PicoScope®2000 series)
Parameters Value Unit
Time base
Longest timebase 5000 s/div
Shortest timebase 2 ns/div
Max waveforms per second 8000 Amplitude
Input ranges ±20 m, ±50 m, ±100 m, ±200 m, ±500 m, ±1, ±2, ±5, ±10, ±20
V Figure 2-3 Single DAC Channel Architecture
8 Analog offset range (vertical
position adjustment)
±250 m (20 m to 200 m ranges) ±2.5 (500 m to 2 ranges) ±25 (5 to 20 ranges)
V
Analog offset control accuracy ±1% of offset setting, additional to basic DC accuracy
Table 2-4 The specifications of PicoScope 5444D (Pico®Technology, PicoScope®5000D Series)
Parameters Value Unit
Time base (1 ns/div to 5000 s/div in 39 ranges)
Longest timebase 100 ps/div
Amplitude
Input ranges ±10 m to ±20 full scale, in 11 ranges
V Analog offset range
(vertical position
Analog offset control accuracy
±0.5% of offset setting, additional to basic DC offset accuracy
2.1.3 JTAG board
JTAG (Joint Test Action Group) board is a functional board for motherboard supply. As what is shown in the Fig.2-4, the board concludes 96 pins to connect with the motherboard, two FPGA (Field-Programmable Gate Array) modules, a header and 5 dual supply transceivers with configurable voltage-level shifting.
Figure 2-4 The schematics of JTAG Board (NXP, Schematic of EVA2's JTAG board, 2020)
9 The 4 dual supply transceivers called SN74LVC2T45 are used for asynchronous communication between two data buses.
This dual-bit noninverting bus transceiver uses two separate configurable power-supply rails. The A port shown in the Fig.2-5 is designed to track VCCA. VCCA accepts any supply voltage from 1.5 V to 5.5 V. The B port is designed to track VCCB. VCCB accepts any supply voltage from 1.5 V to 5.5 V.
This allows for universal low-voltage bidirectional translation between any of the 1.8-V, 2.5-V, 3.3-V, and 5-V voltage nodes (Instruments, 2007).
Hence, if the voltage is under the absolute maximum ratings may cause permanent damage to the device which is required to be calibrated. The specifications of those supply transceivers will be depicted in the Table.2-5. However, the VCCA is supplied by SMU which is calibrated while VCCB is supplied by DAC which is required to be calibrated.
Table 2-5 The specifications of supply transceivers(Instruments, 2007)
Parameters Min Max Unit
VCCA supply voltage range 1.5 5.5 V
VCCB supply voltage range 1.5 5.5 V
2.1.4 Power IO module
Power IO module with 96 channels is inserted in the backplane of the EVA2’s motherboard. It takes charge of controlling relays and communicating with PC through I2C. As what has shown in the schematics of PowerIO module, it includes PCA9555, ULN2803 and 24AA512.
The PCA9555 is a 24-pin CMOS (Complementary metal–oxide–semiconductor) device that provides 16 bits of GPIO (General Purpose parallel Input/Output) expansion for I2C-bus I/O Figure 2-5 The Logic Diagram of the
supply transceivers (Instruments, 2007)
Figure 2-6 The schematics of EVA2's PowerIO module (NXP, Schematics of EVA2's PowerIO module, 2020)
10 expanders (NXP, 2017). The ULN2803 is high-voltage, high-current Darlington drivers comprised of eight NPN Darlington pairs. It plays the role of controlling the relays and the schematics is
shown in Fig. 2-6.
The Darlington transistor pair circuit shown in the Fig.2-7 consists of two transistors. The emitter of the input transistor is connected to the base terminal of the output transistor, base and collectors of these transistors are wired together.
Therefore, the current that is amplified by the first transistor then by the second transistor (elprocus, 2020). The collector-emitter saturation voltage decides the worst condition of the circuitry and is required to be calibrated.
Table 2-6 The specification of Power IO (elprocus, 2020)
Parameter Symbol Test condition Typical value Maximum value Unit
An arbitrary waveform generator (AFG) is a piece of electronic test equipment used to generate electrical waveforms (Wikipedia, arbitrary waveform generator, 2020).
EVA2 utilizes the AFG-2225, shown in the Fig.2-8, as analog signal sources which are not calibrated yet. The “uncalibrated” sign is posted on it. AFG-2225 has the functions of AM/FM/PM/FSK/SUM modulation, scanning, burst and frequency counter, which can be applied to various communication fields. The USB host and device interface are equipped with the function of linking the AFG-2225 with other devices, thus providing a more flexible
waveform generation function, which can be used for more practical purposes. By linking to the GW Instek GDS series digital storage oscilloscope (DSO), the waveform of interest can be
captured and reconstructed. Users can also use arbitrary waveform PC software to edit the waveform, and then send it directly to AFG-2225, or save the waveform to a flash drive, and then transfer it to AFG-2225. (Gwinstek, 2020).
Figure 2-8 The AFG which is not calibrated Figure 2-7 The schematics of
ULN2903 (elprocus, 2020)
11 The specification of AFG-2225 will be shown in the Table.2-7.
Table 2-7 The specifications of AFG-2225 (Good Will Instrument Co.)
Parameters value
Output Characteristics
Amplitude Range 1mVpp to 10 Vpp (into 50Ω) 2mVpp to 20 Vpp (open-circuit) 1mVpp to 5 Vpp (into 50Ω) for 20MHz25MHz 2mVpp to 10 Vpp (open-circuit) for 20MHz25MHz
Accuracy ±2% of setting ±1 mVpp (at 1 kHz) Resolution 1mV or 3 digits
Offset Range ±5 Vpk ac +dc (into 50Ω) ±10Vpk ac +dc (Open circuit) ±2.5 Vpk ac +dc (into 50Ω) for 20MHz-25MHz
±5Vpk ac +dc (Open circuit) for 20MHz25MHz Accuracy 2% of setting + 20mV+ 0.5% of amplitude