Datasheet LT1227 (Analog Devices) - 10

LT1227
O U TYPICAL APPLICATI S MUX Amplifier MUX Amplifier
The shutdown function can be effectively used to con- 15V struct a MUX amplifier. A two-channel version is shown, VIN1 + but more inputs could be added with suitable logic. By LT1227 S/D V configuring each amplifier as a unity-gain follower, there OUT – is no loading by the feedback network when the amplifier is off. The open drains of the 74C906 buffers are used to –15V VOUT interface the 5V logic to the shutdown pin. Feedthrough = 1 1.5k VIN from the unselected input to the output is –70dB at 5V 10MHz. The differential voltage between MUX inputs VIN1 and VIN2 appears across the inputs of the shutdown 74C906 device, this voltage should be less than ±5V to avoid turning on the clamp diodes discussed previously. If the 15V inputs are sinusoidal having a zero DC level, this implies that the amplitude of each input should be less than VIN2 + 5V LT1227 S/D P-P. The output impedance of the off amplifier remains high until the output level exceeds approximately 6V – P-P at 10MHz, this sets the maximum usable output level. Switch- –15V ing time between inputs is about 4µs without an external 1.5k pullup. Adding a 10k pullup resistor from each shutdown pin to V+ will reduce the switching time to 2µs but will 5V 5V increase the positive supply current in shutdown by 1.5mA. INPUT SELECT 74HC04 74C906 1227 TA04
MUX Output MUX Input Crosstalk vs Frequency
–40 –50 VOUT –60 –70 INPUT INPUT CROSSTALK (dB) SELECT –80 –90 TA03 V 1 10 100 IN1 = 1VP-P, VIN2 = 0V FREQUENCY (MHz) LT1227 TA05 10