Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-16
Gibbs, TK: AUTHOR [+1]
A digital-to-analog (D/A) circuit, low in component count and production costs, designed primarily to be compatible with an existing range of monitors is described.
digital-to-analog (D/A) circuit, low in component count
and production costs, designed primarily to be compatible with an
existing range of monitors is described.
disclosure describes a low-cost digital-to-analog
converter which achieves the same level of performance of its
contemporaries but with fewer components. This area of monitor
circuitry has an important impact on the RFI (Radio Frequency
Interference) performance of the system. A reduced component count
will not only make a product more cost effective but will ease the
problems of RFI. Because three channels per monitor are needed, the
circuit savings are increased three-fold per monitor.
Circuit Fig. 1 shows an existing D/A circuit used on
current products. Z1 provides a stable reference source for IC1. IC1
maintains a fixed potential on Q1 base. The current flowing in Q1
is set by the value of R1. Negative feedback is provided by the
voltage dropped across R4. The network Q2, R2 is also driven by IC1.
A defined current will flow in the termination resistance R3. The
digital input signal is fed in via CR1. The analog voltage V must be
able to fall to zero. The saturated Vout of the drive IC and the Vf
of the diode CR1 must be balanced by the inclusion of CR1 and CR2.
Fig. 2 shows the new circuit. Here Z1
the reference voltage which directly controls the potential on Q2