THAT2180A Datasheet, PDF (5/8 Pages) List of Unclassifed Manufacturers – Pre-Trimmed IC Voltage Controlled Amplifiers

600029 Rev 01
Page 5
Figure 8 shows the effect of temperature on the nega-
tive control port. (The positive control port behaves in the
same manner.) Note that the gain at Ec = 0 V is 0 dB, re-
gardless of temperature. Changing temperature changes
the scale factor of the gain by 0.33%/°C, which pivots the
curve about the 0 dB point.
Mathematically, the 2180's gain characteristic is
Gain =
E_C+ - E_C-
,
(0.0061)(1 + 0.0033DT)
Eq. 1
where DT is the difference between room temperature
(25°C) and the actual temperature, and Gain is the
gain in decibels. At room temperature, this reduces to
Gain = ^{EC+ - EC-} ,
0.0061
Eq. 2
If only the positive control port is used, this becomes
Gain = ^EC+ ,
0.0061
Eq. 3
If only the negative control port is used, this becomes
Gain = ^-EC- ,
0.0061
Eq. 4
DC Bias Currents
The 2180 current consumption is determined by the
resistor between pin 5 (V-) and the negative supply voltage
(V_EE). Typically, with 15V supplies, the resistor is 5.1 kW,
which provides approximately 2.4 mA. This current is
split into two paths: 570 mA is used for biasing the IC,
and the remainder becomes Icell as shown in Figure 5.
Icell is further split in two parts: about 20 mA biases the
core transistors (Q1 through Q4), the rest is available for
input and output signal current
DC Feedthrough
Normally, a small dc error term flows in pin 8 (the
output). When the gain is changed, the dc term changes.
This control-voltage feedthrough is more pronounced
with gain; the –A version of the part produces the least
feedthrough, the –C version the most. See Figure 9 for
typical curves for dc offset vs. gain
Audio Performance
The 2180-Series VCA design, fabrication and testing
ensure extremely good audio performance when used as
recommended. In particular, the 2180 maintains low
distortion over a wide range of gain, cut and signal lev-
els. Figures 10 through 12 show typical distortion per-
formance for representative samples of each grade of the
part. Figure 13 shows the harmonic content of the dis-
tortion in a typical B-grade part.
Figure 10. 1 kHz THD+Noise Vs. Input Level, 0 dB Gain
Figure 11. 1 kHz THD+Noise Vs. Input Level,
+15 dB Gain
Figure 12. 1 kHz THD+Noise Vs. Input Level,
-15 dB Gain
Figure 9. Representative DC Offset Vs. Gain
Figure 13. FFT of THD, 0dB gain, 1kHz, 0dBV,
Typical 2180B
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