2180-DEMO THAT Corporation, 2180-DEMO Datasheet - Page 5

• Manufacturer Part Number: 2180-DEMO
• Description: Audio Modules & Development Tools Pre-Trimmed VCA Demo Board
• Manufacturer: THAT Corporation

Specifications of 2180-DEMO

• Description/function: Audio Amplifiers
• Operating Supply Voltage: 15 V
• Product: Audio Modules
• For Use With/related Products: THAT2180
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THAT 2180 Series
Blackmer® Pre-trimmed IC VCAs
negative control port. Because of the exponential
characteristic, the control voltage sets gain linearly
in decibels. Figure 6 shows the decibel current gain
of a 2180 versus the voltage at Ec+, while Figure 7
shows gain versus the Ec-.
Temperature Effects
on the logarithmic relationship between voltage and
current in a semiconductor junction (in particular,
between a transistor's V
this relationship is temperature dependent. There-
fore, the gain of any log-antilog VCA depends on its
temperature.
negative control port. (The positive control port behaves
in the same manner.) Note that the gain at Ec = 0 V is
0 dB, regardless of temperature. Changing temperature
changes the scale factor of the gain by 0.33%/°C, which
pivots the curve about the 0 dB point.
The logging and antilogging in the VCA depends
Figure 8 shows the effect of temperature on the
where ∆T 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
If only the positive control port is used, this
becomes
If only the negative control port is used, this
becomes
Mathematically, the 2180's gain characteristic is
Gain =
Gain =
Gain =
Gain =
(0.0061)(1+0.0033 T)
E
0.0061
0.0061
E
C+
0.0061
E
C+
C−
− E
E
C+
C−
,
,
− E
,
C−
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
be
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
and I
,
c
). As is well known,
Copyright © 2008, THAT Corporation
Eq. 1
Eq. 2
Eq. 3
Eq. 4
Page 5 of 12
DC Bias Currents
the resistor between pin 5 (V-) and the negative
supply voltage (V
resistor is 5.1 kΩ, which provides approximately
2.4 mA. This current is split into two paths: 570 μA
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 μA biases the core
transistors (Q1 through Q4), the rest is available for
input and output signal current.
DC Feedthrough
(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
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 levels. Figures 10 through 12 show
typical distortion performance for representative
samples of each grade of the part. Figure 13 shows
the harmonic content of the distortion in a typical
B-grade part.
The 2180 current consumption is determined by
Normally, a small dc error term flows in pin 8
The 2180-Series VCA design, fabrication and
Figure 9. Representative DC Offset vs. Gain
EE
). Typically, with 15V supplies, the
Document 600029 Rev 02