| 摘要 |
<p>A digital-to-analog converter circuit (10) comprises a current switch (22) that has differential input conductors (16a, 16b, ..., 16n and 18a, 18b, ..., 18n) which receive complementary logic voltage signals corresponding to a digital input word (X1, X2, ..., Xn). The current switch synthesizes an output signal (V0 - @@ ) whose magnitude corresponds to the weighted value of the digital input word. The circuit further comprises a current reference source (60) that develops a reference current (IREF) from which transistor constant-current sources (48a, 48b, ..., 48n) in the current switch derive binary-weighted currents to synthesize the output voltage signal. The current reference source includes an impedance element or resistor (70) through which the reference current flows and which is scaled to the load impedance connected to the current switch. The impedance element compensates for digital-to-analog converter gain dependence associated with the effect of the Early voltage and beta on the output impedance of the transistors forming the current switch. The presence of the impedance element promotes, therefore, stable, uniform changes in the magnitude of the output voltage signal in response to incremental changes in the weighted value of the digital input word.</p> |
