The AD604 is an ultralow noise, very accurate, dual-channel, linear-in-dB variable gain amplifier (VGA) optimized for time-based variable gain control in ultrasound applications; however, it supports any application requiring low noise, wide bandwidth, variable gain control. Each channel of the AD604 provides a 300 kΩ input resistance and unipolar gain control for ease of use. User determined gain ranges, gain scaling (dB/V), and dc level shifting of output further optimize performance.

Each channel of the AD604 utilizes a high performance preamplifier that provides an input referred noise voltage of 0.8 nV/√Hz. The very accurate linear-in-dB response of the AD604 is achieved with the differential input exponential amplifier (DSX-AMP) architecture. Each of the DSX-AMPs comprise a variable attenuator of 0 dB to 48.36 dB followed by a high speed fixed gain amplifier. The attenuator is a 7-stage R-1.5R ladder network. The attenuation between tap points is 6.908 dB and 48.36 dB for the ladder network.

The equation for the linear-in-dB gain response is

G(dB) = (Gain Scaling (dB/V) × VGN (V))

+ (Preamp Gain (dB) – 19 dB)

Preamplifier gains between 5 and 10 (14 dB and 20 dB) provide overall gain ranges per channel of 0 dB through 48 dB and 6 dB through 54 dB. The two channels of the AD604 can be cascaded to provide greater levels of gain range by bypassing the second channel’s preamplifier. However, in multiple channel systems, cascading the AD604 with other devices in the AD60x VGA family that do not include a preamplifier may provide a more efficient solution. The AD604 provides access to the output of the preamplifier, allowing for external filtering between the preamplifier and the differential attenuator stage.

Note that scale factors up to 40 dB/V are achievable with reduced accuracy for scales above 30 dB/V. The gain scales linearly-in-dB with control voltages of 0.4 V to 2.4 V with the 20 dB/V scale. Below and above this gain control range, the gain begins to deviate from the ideal linear-in-dB control law. The gain control region below 0.1 V is not used for gain control. In fact when the gain control voltage is <50 mV, the amplifier channel is powered down to 1.9 mA.

The AD604 is available in 24-lead SSOP, SOIC, and PDIP packages and is guaranteed for operation over the −40°C to +85°C temperature range.

Applications

Ultrasound and sonar time gain control

High performance AGC systems

Signal measurement

Data Sheet, Rev. D, 1/08

Part#	Gain Control	-3 dB BW (MHz)	Gain Low End (dB)	Gain High End (dB)	Number of Channels	Spectral Noise (nV/rtHz)	Supply Voltage (V)	Supply Current (max)	Gain Accuracy (dB)	1 dB Comp Point (dBm)	Package	Price* (1000-4999)
AD600	Analog	35	0	+40	2	1.4	±5	14mA	-	-	-	$16.41
AD602	Analog	35	-10	+30	2	1.4	±5	14mA	-	-	-	$13.20
AD603	Analog	90	-11	+31	1	1.4	±5	20mA	±0.5	-	8-Lead DIP, 8-Lead SOIC	$4.35
AD604	Analog	40	0	+48	2	0.8	±5	31mA	±0.3	15	24-Lead SOIC, 24-Lead SSOP	$16.25
AD605	Analog	40	-14	+34	2	1.8	+5	23mA	±0.2	15	16-Lead SOIC	$9.79
AD8260	Digital	180	-6	+24	1	2.4	+3.3	28mA	+0.25	-	-	$3.79
AD8320	Digital	150	-10	+26	1	53	+12	105mA	±0.2	22.5	20-Lead SOIC	-
AD8321	Digital	120	-27.4	+26	1	20	+9	90mA	±1	19.5	20-Lead SOIC	$4.35
AD8322	Digital	180	-12.6	+29.5	1	64	+5	113mA	±2	19	28-Lead TSSOP	$3.15
AD8323	Digital	100	-26	+27.5	1	-	+5	-	-	-	28-Lead TSSOP	$3.30
AD8324	Digital	100	-25.5	+33.5	1	157	+3.3	207mA	±1	21	20-Lead LFCSP, 20-Lead QSOP	$1.71
AD8325	Digital	100	-29.5	+30	1	56	+5	133mA	±1	18.5	28-Lead TSSOP	$3.30
AD8326	Digital	100	-26	+27.5	1	100	±5	157mA	±1	26.5	28-Lead PSOP, 28-Lead TSSOP	$3.90
AD8327	Digital	160	-18	+30	1	64	+5	105mA	±1	18	20-Lead TSSOP	$3.75
AD8328	Digital	107	-27.5	+31.5	1	135	-	120mA	±1	18.4	20-Lead LFCSP, 20-Lead QSOP	$1.90
AD8330	Analog	150	0	+50	1	5	+6	20mA	±0.5	-	16-Lead LFCSP, 16-Lead QSOP	$4.39
AD8331	Analog	120	-4.5	+43	1	0.74	+5	25mA	+0.5	7	-	$5.39
AD8332	Analog	120	-4.5	+43.5	2	0.74	+5	58mA	+0.5	7	28-Lead TSSOP, 32-Lead CSP	$10.44
AD8334	Analog	100	+4.5	+43.5	4	0.74	+5	116mA	+0.5	7	64-Lead LFCSP	$14.49
AD8335	Analog	70	-10	+38	4	1.3	+5	76mA	±0.2	18	64-Lead LFCSP	$12.00
AD8336	Analog	115	-14	+46	1	3	±12	25mA	±0.5	11	16-Lead LFCSP	$4.59
AD8337	Analog	280	0	+24	1	2.2	±5	15mA	±0.25	-	8-Lead LFCSP	$2.49
AD8367	Analog	500	-2.5	+42.5	1	1.84	+5.5	26mA	±0.2	8.1	14-Lead TSSOP	$4.55
AD8368	Analog	800	-12	+22	1	-	+5	-	±0.4	13	24-Lead LFCSP	$4.55
AD8369	Digital	600	-5	+40	1	2	+5.5	37mA	±0.5	0.5	16-Lead TSSOP	$4.20
AD8370	Digital	700	+25	+34	1	2.1	+5.5	78mA	-	14	16-Lead TSSOP	$4.20
AD8375	Digital	690	-4	+20	1	-	+5	130mA	±0.2	19	24-Lead LFCSP	$4.49
AD8376	Digital	690	-4	+20	2	-	+5	260mA	±0.2	19	32-Lead CSP	$6.49
ADL5330	Analog	3000	-34	+22	1	-	+5	240mA	-	1.2	24-Lead LFCSP	$4.98
ADL5390	Analog	2400	-	+7	1	-	+5	130mA	-	9.6	24-Lead LFCSP	$7.50
ADL5391	Analog	2000	-	+9.5	1	26.7	+5	135mA	-	15.1	16-Lead LFCSP	$4.89

* The pricing listed here is provided only for budgetary purposes as recommended list price in U.S. Dollars in the United States ex factor per unit for the stated volume. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.
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