Ece 353 Digital Microelectronics

ECE 353 DIGITAL MICROELECTRONICS

LABORATORY EXPERIMENT #2

MEASUREMENT OF LOGIC FAMILY VOLTAGE TRANSFER CHARACTERISTICS

GOAL:

To observe the static behavior of several logic families. To measure the following: voltage transfer characteristic (VTC) , Vol, Voh, Vilmax, Vihmin, DCNM(0), DCNM(1), and static power dissipation (Pdiss)..

EQUIPMENT AND SUPPLIES:

Agilent 33120A Synthesized Function Generator

Agilent E3631A Power Supply

Agilent 54616C Digital Oscilloscope with two probes

Prototyping Board and wires

74xx04 hex inverters of several families and 74LS14 Hex Schmitt Trigger

Bypass capacitors (0.01 F or 0.1 F monolythic or disk ceramic)

50  resistor (can use two 100  resistors in parallel if 50  is not available)

SETUP:

To measure the VTC we will construct a simple voltage-voltage curve tracer. Our input will be a low-frequency 0-to-5 V triangular wave signal from the function generator and we will use the oscilloscope in the X-Y mode to display the input voltage (on the X axis) and the output voltage (on the Y axis) of a device under test (DUT). The setup is diagrammed below:

Figure 1

Caution: Many logic families can be damaged if a low-impedance voltage source drives an input to above or below the supply voltages (i.e. above Vcc or Vdd, or below Vss or ground). Try to keep the input voltage in a range between the supply voltage "rails" (negative and positive supply voltages).

Setup the power supply to deliver 5V (on the 0-6V output) with a current limit value of 100 mA as follows: Press +6 Vto select the 0-6 V supply channel; press Display Limit, and set the voltage to +5.000; press Voltage/Current to select the current-limit value and enter a value of 100 mA. If the current begins to exceed the limit value which you have set,the power supply automatically reduces ("folds back") the voltage to limit the current to the set value. This protects the DUT.

Setup the function generator to deliver a triangular wave signal at 100 Hz from 0 to +5 V. To do this you will generate a 5 Vpp (Volts peak-to-peak) waveform with a dc offset of +2.5 V. Note that the Agilent 33120A function generator has an output resistance of 50  and is designed to drive a 50  load. This is common and convenient when coaxial cable transmission lines having a 50  characteristic resistance are being driven; it helps prevent reflections from propagating on the transmission line. For our purposes we will need to supply a 50  resistor as a load; if we don't the voltage output by the function generator will be twice as high as desired! Use the oscilloscope to check that the voltage waveform is indeed sweeping between 0 and +5 volts.

On the oscilloscope, now select the X-Y display function as follows: press Main/Delayed and then the XY softkey (below the display). Set both the vertical and horizontal sensitivities to 1 V/Div. Finish connecting the scope as shown in Figure 1.

You can use the Auto Store function on the scope and reduce the function generator frequency to 1 Hz if you want to view the transfer characteristic being swept. This is especially useful when viewing the Schmitt Trigger VTC. The Erase button on the scope clears the stored display.

LAB ASSIGNMENT:

Note: If the printer in the lab roomis setup you can print the display rather than sketch it.

1)Measure and sketch the no-load VTCs of one inverter of:

7404 (standard TTL)

74LS04 (low-power Schottky TTL)

74S04 (Schottky TTL)

74F04 (FAST Schottky TTL)

74C04 (CMOS)

74HC04 (high-speed CMOS)

Also record the supply current (from the power supply readout). Calculate and record the static power dissipation Pdiss of each package of six inverters. Comment on the relative power dissipations, keeping in mind that the power dissipations would be higher when switching at high frequencies.

From the VTC estimate and record Vol, Voh, Vilmax, Vihmin, DCNM(0), DCNM(1).

NOTE that if you observe oscillations you may need to add bypass capacitors on Vcc (Vdd) to Vss (GND), and a slow-down capacitor on the gate input or output. This is especially likely on the faster families or families with a very high gain (high negative slope) in the transition region of the VTC.

2)Measure and sketch the no-load VTC of one inverter of a 74LS14 Hex Schmitt Trigger Inverter. You may decrease the function generator frequency to 1 Hz and use the storage function of the scope to view the sequence of events more clearly. Explain your observations. Measure and record the hysteresis voltage (see the databook in the lab room or find the specs on the web for a description of this component). What practical uses might this component have?

3)Connect one inverter of a 74LS04 as the DUT, and connect an increasing number of 7404 inverters as loads. Record the changes in Vol and V0h as the number of loads increases. Experimentally, what is the maximum static fanout for LS TTL driving TTL? According to the specs, what is the maximum guaranteed fanout for this combination? Why might the static fanout which you measure be greater than the fanout specified?

4)Repeat (3) for a 74C04 driving 7404.