Datasheet LT1194 (Analog Devices) - 8

LT1194
U U W U APPLICATIO S I FOR ATIO
A scope photo of the amplifier output with no supply
Settling Time Good Bypass
bypassing is used to demonstrate this bypassing toler- ance, RL = 1k. In many applications, and those requiring good settling time, it is important to use multiple bypass capacitors. A 0.1µF ceramic disc in parallel with a 4.7µF tantalum is recommended. Two oscilloscope photos with different bypass conditions are used to illustrate the settling time characteristics of the amplifier. Note that although the output waveform looks acceptable at 1V/DIV, when ampli- fied to 10mV/DIV the settling time to 10mV is 200ns. The time drops to 162ns with multiple bypass capacitors, and LT1194 • TA07 SETTLING TIME TO 10mV, does not exhibit the characteristic power supply ringing. SUPPLY BYPASS CAPACITORS = 0.1µF + 4.7µF TANTALUM
No Supply Bypass Cable Terminations
The LT1194 video difference amplifier has been optimized as a low cost cable driver. The ±50mA guaranteed output current enables the LT1194 to easily deliver 7.5VP-P into 100Ω, while operating on ±5V supplies, or 2.6VP-P on a single 5V supply. When driving a cable it is important to terminate the cable to avoid unwanted reflections. This can be done in one of two ways: single termination or double termination. With single termination, the cable must be terminated at the LT1194 • TA05 receiving end (75Ω to ground) to absorb unwanted en- IN DEMO BOARD, RL = 1k ergy. The best performance can be obtained by double termination (75Ω in series with the output of the amplifier,
Settling Time Poor Bypass
and 75Ω to ground at the other end of the cable). This termination is preferred because reflected energy is ab- sorbed at each end of the cable. When using the double termination technique it is important to note that the signal is attenuated by a factor of 2, or 6dB. For a cable driver with a gain of 5 (LT1194 gain of 10), the –3dB bandwidth is over 30MHz with no peaking.
A Voltage Controlled Current Source
The LT1194 can be used to make a fast, precise, voltage controlled current source. The LT1194 high speed differ- LT1194 • TA06 ential amplifier senses the current delivered to the load. SETTLING TIME TO 10mV, SUPPLY BYPASS CAPACITORS = 0.1µF The input signal VIN, applied to the (+) input of the LT1191, 8