Electronic Components Datasheet Search |
|
AD603AR Datasheet(PDF) 5 Page - Analog Devices |
|
AD603AR Datasheet(HTML) 5 Page - Analog Devices |
5 / 14 page AD603 REV. C –5– The Gain-Control Interface The attenuation is controlled through a differential, high- impedance (50 M Ω) input, with a scaling factor which is laser-trimmed to 40 dB per volt, that is, 25 mV/dB. An internal bandgap reference ensures stability of the scaling with respect to supply and temperature variations. When the differential input voltage VG = 0 V, the attenuator “slider” is centered, providing an attenuation of 21.07 dB. For the maximum bandwidth range, this results in an overall gain of 10 dB (= –21.07 dB + 31.07 dB). When the control input is –500 mV, the gain is lowered by 20 dB (= 0.500 V × 40 dB/V), to –10 dB; when set to +500 mV, the gain is increased by 20 dB, to 30 dB. When this interface is overdriven in either direction, the gain approaches either –11.07 dB (= – 42.14 dB + 31.07 dB) or 31.07 dB (= 0 + 31.07 dB), respectively. The only constraint on the gain-control voltage is that it be kept within the common-mode range (–1.2 V to +2.0 V assuming +5 V supplies) of the gain control interface. The basic gain of the AD603 can thus be calculated using the following simple expression: Gain (dB) = 40 VG + 10 (1) where VG is in volts. When Pins 5 and 7 are strapped (see next section) the gain becomes Gain (dB) = 40 VG + 20 for 0 to +40 dB and Gain (dB) = 40 VG + 30 for +10 to +50 dB (2) The high impedance gain-control input ensures minimal loading when driving many amplifiers in multiple channel or cascaded applications. The differential capability provides flexibility in choosing the appropriate signal levels and polarities for various control schemes. For example, if the gain is to be controlled by a DAC providing a positive only ground-referenced output, the “Gain Control LO” (GNEG) pin should be biased to a fixed offset of +500 mV, to set the gain to –10 dB when “Gain Control HI” (GPOS) is at zero, and to 30 dB when at +1.00 V. It is a simple matter to include a voltage divider to achieve other scaling factors. When using an 8-bit DAC having an FS output of +2.55 V (10 mV/bit), a divider ratio of 2 (generating 5 mV/bit) would result in a gain-setting resolution of 0.2 dB/bit. The use of such offsets is valuable when two AD603s are cascaded, when various options exist for optimizing the S/N profile, as will be shown later. Programming the Fixed-Gain Amplifier Using Pin Strapping Access to the feedback network is provided at Pin 5 (FDBK). The user may program the gain of the AD603’s output amplifier using this pin, as shown in Figure 2. There are three modes: in the default mode, FDBK is unconnected, providing the range +9 dB/+51 dB; when VOUT and FDBK are shorted, the gain is lowered to –11 dB/+31 dB; when an external resistor is placed between VOUT and FDBK any intermediate gain can be achieved, for example, –1 dB/+41 dB. Figure 3 shows the nominal maxi- mum gain versus external resistor for this mode. GPOS GNEG VINP COMM VPOS VOUT VNEG FDBK AD603 VC1 VC2 VIN VPOS VOUT VNEG a. –10 dB to +30 dB; 90 MHz Bandwidth GPOS GNEG VINP COMM VPOS VOUT VNEG FDBK AD603 VC1 VC2 VIN VPOS VOUT VNEG 2.15k 5.6pF b. 0 dB to +40 dB; 30 MHz Bandwidth GPOS GNEG VINP COMM VPOS VOUT VNEG FDBK AD603 VC1 VC2 VIN VPOS VOUT VNEG 18pF c. +10 dB to +50 dB; 9 MHz Bandwidth Figure 2. Pin Strapping to Set Gain REXT 52 10 1M 100 1k 10k 100k 50 48 46 44 42 40 38 36 34 32 30 –1:VdB (OUT) –2:VdB (OUT) VdB (OUT) Figure 3. Gain vs. REXT, Showing Worst-Case Limits Assuming Internal Resistors Have a Maximum Tolerance of 20% |
Similar Part No. - AD603AR |
|
Similar Description - AD603AR |
|
|
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 |