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ADRF5474BCZ データシート(PDF) 11 Page - Analog Devices |
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ADRF5474BCZ データシート(HTML) 11 Page - Analog Devices |
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11 / 14 page  Data Sheet ADRF5474 THEORY OF OPERATION analog.com Rev. 0 | 11 of 14 The ADRF5474 incorporates a 4-bit fixed attenuator array that offers an attenuation range of 22 dB in 2 dB steps. An integrated driver provides parallel mode control of the attenuator array. The ADRF5474 has four digital control inputs, D2 (LSB) to D5 (MSB), to select the desired attenuation state in parallel mode, as shown in Figure 23. Internally, there are two 8 dB stages, and these stages can be controlled by the D4 and D5 pins. POWER SUPPLY The ADRF5474 requires a positive supply voltage applied to the VDD pad and a negative supply voltage applied to the VSS pad. Bypassing capacitors are recommended on the supply lines to filter high frequency noise. The power-up sequence is as follows: 1. Connect GND. 2. Power up the VDD and VSS voltages. Power up VSS after VDD to avoid current transients on VDD during ramp up. 3. Power up the digital control inputs. The order of the digital control inputs is not important. However, powering the digital control inputs before the VDD voltage supply can inadvertently forward bias and damage the internal ESD structures. To avoid this damage, use a series 1 kΩ resistor to limit the current flowing into the control pad. 4. Apply an RF input signal to ATTIN or ATTOUT. The power-down sequence is the reverse order of the power-up sequence. Power-Up State The ADRF5474 has an internal pull-up resistor (see Figure 6). The internal pull-up resistor sets the attenuator to the maximum attenuation state (22 dB) when the VDD and VSS voltages are applied. RF INPUT AND OUTPUT Both RF ports (ATTIN and ATTOUT) are dc-coupled to 0 V. No dc blocking is required at the RF ports when the RF line potential is equal to 0 V. The ADRF5474 supports bidirectional operation at a lower power level. The power handling of the ATTIN and ATTOUT ports are different. Therefore, the bidirectional power handling is defined by the ATTOUT port. Refer to the RF input power specifications in Table 1. Table 7. Truth Table Digital Control Input1 Attenuation State (dB) D52 D42 D3 D2 Low Low Low Low 0 (reference) Low Low Low High 2.0 Low Low High Low 4.0 Low Low High High 6.0 Low High Low Low 8.0 Low High Low High 10.0 Low High High Low 12.0 Low High High High 14.0 High High Low Low 16.0 High High Low High 18.0 High High High Low 20.0 High High High High 22.0 1 Any combination of the control voltage input states shown in this table provides an attenuation equal to the sum of the bits selected. 2 D4 and D5 both correspond to the 8 dB state. D4 has slightly better state accuracy at higher frequencies. Figure 23. Simplified Circuit Diagram |
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