CEM3365

Fast Dual DAC Multiplier

Other names for this product: CEM 3365,

Courtesy/Thanks to: CEM

Description: The CEM 3365 is a dual high speed one quadrant multiplier intended to scale the
output of fast bipolar DACs in digital audio applications, such as DCOs. Each half of
the 3365 contains a very fast op amp and a high speed current in/current out gain
cell, whose gain is controlled by the output of the op amp. The settling time for a
full-scale 12-bit excursion is 150ns. Typical (200ns max.) This response is in contrast
to the 10’s of uS which would result from changing the reference input of even the
fastest bipolar multiplying DACs.

As both inputs and outputs of the op amp are externally available, two modes of
operation are possible. One is to configure the op amp as the current-to-voltage
converter of a second bipolar control DAC, so that the gain may be controlled
directly by a digital word. Effective resolution of the result is the sum sum of the
resolutions of the two DACs (24 bits for two 12 bit DACs). The second mode is to
configure the op amp simply as a voltage follower, allowing the gain to be controlled
by a voltage (from a Sample/Hold, for example).

Although the input to the gain cell is limited to unipolar current, the output may be
made bipolar simply by connecting a proper resistor from the op amp output to the
gain cell output. Additional versatility is provided by the reference voltage pin,
which accurately sets the op amp voltage required for maximum gain.

A typical application for the 3365 would be to control the amplitude of digitially
generated audio signals in a multiplexed system. When used with a CEM5510 Fast
Octal S/H, 8 channels of digital audio with individual amplitude control at 24 bits of
resolution can be generated.

Fast, flexible, and requiring few support components, the CEM3365 offers an
inexpensive alternative to the high speed hardware digital multipliers required in
multiplexed digital audio systems.

FEATURES

· Fast multiplication of bipolar DAC outputs: settling tine < 200ns.

· Gain controllable by another DAC or by a control voltage

· Two independent multipliers in a single 14 pin DIP package

· Adjustable voltage level required for maximum gain