Os motores de busca de Datasheet de Componentes eletrônicos |
|
DAC908E Folha de dados(PDF) 11 Page - Burr-Brown (TI) |
|
|
DAC908E Folha de dados(HTML) 11 Page - Burr-Brown (TI) |
11 / 15 page ® DAC908 11 The value of the load resistance is limited by the output compliance specification of the DAC908. To maintain speci- fied linearity performance, the voltage for IOUT and IOUT should not exceed the maximum allowable compliance range. The two single-ended output voltages can be combined to find the total differential output swing: (7) ANALOG OUTPUTS The DAC908 provides two complementary current outputs, IOUT and IOUT. The simplified circuit of the analog output stage representing the differential topology is shown in Figure 2. The output impedance of 200k Ω || 12pF for I OUT and IOUT results from the parallel combination of the differ- ential switches, along with the current sources and associ- ated parasitic capacitances. IOUT and IOUT. Furthermore, using the differential output configuration in combination with a transformer will be instrumental for achieving excellent distortion performance. Common-mode errors, such as even-order harmonics or noise, can be substantially reduced. This is particularly the case with high output frequencies and/or output amplitudes below full-scale. For those applications requiring the optimum distortion and noise performance, it is recommended to select a full-scale output of 20mA. A lower full-scale range down to 2mA may be considered for applications that require a low power consumption, but can tolerate a reduced performance level. FIGURE 2. Equivalent Analog Output. The signal voltage swing that may develop at the two outputs, IOUT and IOUT, is limited by a negative and positive compliance. The negative limit of –1V is given by the breakdown voltage of the CMOS process, and exceeding it will compromise the reliability of the DAC908, or even cause permanent damage. With the full-scale output set to 20mA, the positive compliance equals 1.25V, operating with +VD = 5V. Note that the compliance range decreases to about 1V for a selected output current of IOUTFS = 2mA. Care should be taken that the configuration of DAC908 does not exceed the compliance range to avoid degradation of the distortion performance and integral linearity. Best distortion performance is typically achieved with the maximum full-scale output signal limited to approximately 0.5V. This is the case for a 50 Ω doubly terminated load and a 20mA full-scale output current. A variety of loads can be adapted to the output of the DAC908 by selecting a suitable transformer while maintaining optimum voltage levels at OUTPUT CONFIGURATIONS The current output of the DAC908 allows for a variety of configurations, some of which are illustrated below. As mentioned previously, utilizing the converter’s differential outputs will yield the best dynamic performance. Such a differential output circuit may consist of an RF transformer (see Figure 3) or a differential amplifier configuration (see Figure 4). The transformer configuration is ideal for most applications with ac coupling, while op amps will be suitable for a dc-coupled configuration. The single-ended configuration (see Figure 6) may be con- sidered for applications requiring a unipolar output voltage. Connecting a resistor from either one of the outputs to ground will convert the output current into a ground-refer- enced voltage signal. To improve on the dc linearity an I to V converter can be used instead. This will result in a negative signal excursion and, therefore, requires a dual supply amplifier. DIFFERENTIAL WITH TRANSFORMER Using an RF transformer provides a convenient way of converting the differential output signal into a single-ended signal while achieving excellent dynamic performance (see Figure 3). The appropriate transformer should be carefully selected based on the output frequency spectrum and imped- ance requirements. The differential transformer configura- tion has the benefit of significantly reducing common-mode signals, thus improving the dynamic performance over a wide range of frequencies. Furthermore, by selecting a suitable impedance ratio (winding ratio), the transformer can be used to provide optimum impedance matching while controlling the compliance voltage for the converter outputs. The model shown, ADT1-1WT (by Mini-Circuits), has a 1:1 ratio and may be used to interface the DAC908 to a 50 Ω load. This results in a 25 Ω load for each of the outputs, I OUT and IOUT. The output signals are ac coupled and inherently isolated because of the transformer's magnetic coupling . INPUT CODE (D7 - D0) IOUT IOUT 1111 1111 20mA 0mA 1000 0000 10mA 10mA 0000 0000 0mA 20mA Table I. Input Coding vs Analog Output Current. VV V Code IR OUTDIFF OUT OUT OUTFS LOAD == • •• – (– ) 2 255 256 I OUT I OUT DAC908 R L R L +V A |
Nº de peça semelhante - DAC908E |
|
Descrição semelhante - DAC908E |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |