Electronic Components Datasheet Search |
|
CMX993 Datasheet(PDF) 11 Page - CML Microcircuits |
|
CMX993 Datasheet(HTML) 11 Page - CML Microcircuits |
11 / 26 page Quadrature Modulator CMX993/CMX993W 2013 CML Microsystems Plc 11 D/993/10 5 General Description The CMX993 and CMX993W are RF quadrature modulators with additional features such as gain control and uncommitted differential amplifiers. Detailed block diagrams for the ICs are shown in section 2. The ICs can support a wide range of modulation formats and standards including TDMA operation. The following sections describe the functionality of the ICs. 5.1 Quadrature Modulator The quadrature modulator provides translation from baseband I and Q signals to a modulated RF signal. The wideband inputs can be driven differentially or single-ended. In the case of single ended operation a reference voltage equal to the nominal dc level of the modulation must be supplied. The input and filter amplifiers allow single-ended signals to be translated to an appropriate dc level, one solution for an input signal with 0V dc bias is shown in Figure 4/4a. 5.1.1 DC Offsets and Carrier Leakage The modulator inputs (MODIN/MODIP and MODQN/MODQP) are differential and require a common dc level or common mode voltage. Differences in the bias voltages on the pins will result in an increased level of carrier present at the output. Care should be taken to minimise offsets, thereby minimising carrier leakage. Some systems implement carrier nulling before transmission. This results in a compensation of the small internal offsets in the modulator and any offsets generated in external circuits. Digital to analogue converters designed for I/Q systems, e.g. CMX981, often include registers which allow a programmable offset to be applied to the I/Q signals, making this nulling process straightforward. 5.1.2 Wideband Noise and Gain Control The wideband noise of this modulator is optimised to ensure a low noise floor at the output, compliant with common product standards. This stage also provides gain control, which allows the output level to be adjusted while maintaining the maximum possible signal-to-noise ratio. To ensure optimum performance the I/Q input signals need to be free from noise. The input bandwidth of the modulators is quite broad, so any noise on the I/Q signals will get translated to the RF output. Such noise can generally be removed by simple RC filters, as shown in Figure 4/4a. Careful attention needs to be paid to the bandwidth of these filters as, if unduly narrow, they can affect the modulation, degrading image rejection and modulation accuracy. 5.2 Differential Amplifiers 5.2.1 Input Amplifiers Two differential amplifiers are provided which may be used for signal conditioning, for example conversion of differential input signals to single ended format, or to provide dc level translation. The amplifiers are uncommitted, with the differential inputs and the output all available on pins. The stages are low power and are enabled using the ‘General Control Register’ (see section 6.2). It is not possible to independently control each amplifier, both are enabled with a common control bit. |
Similar Part No. - CMX993 |
|
Similar Description - CMX993 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |