that2155 ETC-unknow, that2155 Datasheet - Page 7

• Manufacturer Part Number: that2155
• Description: Voltage-controlled Amplifiers
• Manufacturer: ETC-unknow

Input
currents, not voltages. While this often causes some
conceptual difficulty for designers first exposed to this
convention, the current input/output mode provides
great flexibility in application.
tive feedback provided internally (see Figure 6, Page 4).
The input resistor (shown as 20 k
should be scaled to convert the available ac input volt-
age to a current within the linear range of the device.
(Peak input currents should be kept under 1 mA for
best distortion performance.) An additional consider-
ation is stability: the internal op amp is intended for
operation with source impedances of less than 30 k
at high frequencies. For most audio applications, this
will present no problem.
tle effect on distortion. Since the feedback impedances
around the internal opamp (essentially Q1/D1 and
Q3/D3) are fixed, low values for the input resistor will
require more closed-loop gain from the opamp. Since
Figure 12. 1kHz THD+Noise Vs. Input, +15 dB Gain
Figure 10. 1kHz THD+Noise Vs. Input, -15 dB Gain
Rev. 10/25/96
As mentioned above, input and output signals are
The input pin (pin 1) is a virtual ground with nega-
The choice of input resistor has an additional, sub-
THAT Corporation; 734 Forest Street; Marlborough, Massachusetts 01752; USA
Tel: [phone]; Fax: [phone]; Web: http://www.thatcorp.com
in Figure 3, Page 3)
Applications
the open-loop gain naturally falls off at high frequen-
cies, asking for too much gain will lead to increased
high-frequency distortion. For best results, this resis-
tor should be kept to 10 k
quency for a 1 V signal at 0 dB gain with a 20 k
resistor is plotted in Figure 13.
proximately +10 mV. As mentioned above, any dc input
currents will cause dc signals in the output which will
be modulated by gain, causing audible thump. There-
The quiescent dc voltage level at the input is ap-
Figure 11. 1kHz THD+Noise Vs. Level, 0 dB Gain
Figure 13. THD Vs. Frequency, 0 dB Gain
or above. Distortion vs. fre-
Page 7
input