jeff shelton 3 february 2015 - purdue university
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Jeff Shelton – 3 February 2015
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Device One Device Two
⇒ Device Two reads exactly “0”
⇒ Device Two reads exactly “1”
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Jeff Shelton – 3 February 2015
tpHL tpLH
VIN
VOUT
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Device One Device Two
Noise
⇒ Device Two may read a “0” or “1”
⇒ Device Two may read a “1” or “0”
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Output
Input
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Noise Margin
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Output
Input
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Guaranteed Voltages Noise MarginFamily
VIH VOH VIL VOL High (1) Low (0)
74 TTL 2.0 2.4 0.8 0.4 0.4 0.4
74LS TTL 2.0 2.7 0.8 0.5 0.7 0.3
74ALS TTL 2.0 2.7 0.8 0.5 0.7 0.3
74F TTL (Fast) 2.0 2.7 0.8 0.5 0.7 0.3
Hi-Speed CMOS 3.5 4.9 1.0 0.1 1.4 0.9
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"Sinking" Output Provides a path to ground
"Sourcing" Output Provides a path from voltage source
Devices often have unequal capacities for sinking and sourcing current
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Vin = HIGH
Vout = LOW
Vcc
Vin = LOW
Vout = HIGH
Vcc V+ V+
Jeff Shelton – 3 February 2015
Vin = HIGH
Vout = LOW
Vcc
Vin = LOW
Vout = HIGH
Vcc V+
"Sourcing" Input Provides a path from voltage source
"Sinking" Input Provides a path to ground
Sinking and sourcing of current is a device-specific phenomenon
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V+
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Currents going into device are considered positive
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2
…
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IOH= 400 uA IIH= 40 uA
IIH= 40 uA
IIH= 40 uA
"HIGH"
"SOURCING" OUTPUT
"SINKING" INPUT
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2
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IOL= 16 mA IIL= 1.6 mA
IIL= 1.6 mA
IIL= 1.6 mA
"LOW"
"SINKING" OUTPUT
"SOURCING" INPUT
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Input Sourcing current (mA)
Output Sinking current (mA)
Input Sinking current (mA)
Output Sourcing current (uA)
Jeff Shelton – 3 February 2015 16 Compatible w/ TTL Voltages!
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Very low static power consumption!
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•
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Can Q3 safely sink the necessary current?
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Vcc
Bus
Output
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7414 – Hex Inverter with Schmitt Trigger Inputs
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Image: https://i.cmpnet.com/planetanalog/2006/04/C0039-Figure%201.jpg
DIP (Dual Inline Package) SMD (Surface Mount Device)
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