1 video ics stereo microphone amplifier for cam- corders BA7781k the BA7781k allows construction of a stereo-microphone amplifier for camcorder use with a minimum number of external components. the ic has a built-in wind-noise detection circuit, and wind-noise rejection filter. the filter cir- cuit is controlled automatically. the ic can operate off a 3.0v power supply. applications camcorders features 1) operates off a 3.0v to 5.25v power supply. 2) automatic wind-noise rejection circuit. 3) matrix circuit for stereo emphasis. 4) automatic switching circuit for external micro- phones, built-in external monaural decision circuit, and input switch mode decision circuit. block diagram 04 05 06 24 23 22 18 17 16 15 14 12 11 09 25 26 27 28 29 30 31 32 13 10 01 02 03 07 08 21 20 19 ext in l bg int in l gnd vreg int in r ripl ext in r det out det in bias v cc lpf inv out lpf inv in mix out mic mono mode 24 pre out l inv in l inv out l mtx in l mtx out l hpf in l out l mode 1 pre out r inv in r inv out r mtx in r mtx out r hpf in r out r ext int 13db 13db gnd reg bias int ext + ? nor wnd nor wnd 15db ? ext ext bias v cc mix + ? 10db 15db ? + det +
2 video ics BA7781k absolute maximum ratings (ta = 25?) parameter symbol limits unit v cc 7.0 v pd mw topr c tstg c 400 * ? 10 ~ +70 ? 55 ~ +125 * reduced by 4mw for each increase in ta of 1 c over 25 c. power supply voltage power dissipation operating temperature storage temperature recommended operating conditions (ta = 25?) parameter symbol min. typ. max. unit v ccs 3.0 5.25 v power supply voltage electrical characteristics (unless otherwise noted, ta = 25? and v cc = 3.3v) parameter symbol min. typ. max. unit i int 5.0 8.0 ma i ext 4.8 8.0 ma vg pr 12 13 14 db vg oa 14 15 16 db thd 0.05 0.3 % v om 0.85 1.1 v rms vno ? 90 ? 80 dbv ct i ? e ? 88 ? 70 db ? 61 ? 50 db v reg 2.3 2.5 2.75 v v hswh 1.6 v cc v v hswl 0 0.6 v vg hon ? 30 db vg hoff ? 30 db v hon 2.5 v v hoff 0 0.3 v ct l ? ? r conditions v cc int mic in, l / rch ext mic in, l / rch 30 / 32pin ? 2pin gain 27 / 25pin ? 23pin gain 3 / 6 / 7pin ? 8pin gain 22 / 19 / 18pin ? 17pin gain int / ext, vo = 300mv rms , l / rch * 2 int / ext mic in, l / rch int / ext, l / rch, r g = 1k w int / ext mic, lch ? rch, r g = 1k w 15pin ? 29.0dbv in (80hz ) 6 / 19pin ? 25.5dbv in (1khz ) 6 ? 8pin / 19 ? 17pin gain 15pin ? 45.0dbv in (80hz ) 7 / 18pin ? 25.5dbv in (1khz) 7 ? 8pin / 18 ? 17pin gain int ? ext mic in, r g = 1k w , l / rch current dissipation 1 current dissipation 2 preamplifier gain output amplifier gain distortion maximum output voltage output noise voltage input switch separation interchannel separation internal microphone power supply voltage input switch control voltage high-pass filter switching attenuation characteristic high-pass filter control voltage * 1 jis-a filter used. * 2 400hz to 30khz filter used. no dissipation by mic no dissipation by mic f = 1khz ( distortion 1% * 2 ) when gain is 28db * 1 (distortion 1% * 2 ) , when gain is 28db * 1 (distortion 1% * 2 ) , when gain is 28db * 1 pin 27 output voltage for 30k w load ??evel, 1 / 24 pin dc ??level, 1 / 24 pin dc input 80hz signal to pin 15, and measure gain at switch off side. * 1 hpf on holding voltage (pin 16) hpf off holding voltage (pin 16)
3 video ics BA7781k 1 mode 1 25k w 2 pre out r 1.65 3 inv in r 1.65 100k w 4 inv out r 1.65 5 mtx in r 1.65 b 6 mtx out r 1.65 7 hpf in r 1.65 100k w 8 out r 1.65 9 mic mono c 10 mix out 1.65 11 lpf inv in b 12 lpf inv out 13 v cc 3.3 14 bias 1.65 15 det in 1.65 2k w 16 det out 22k w 17 out l 1.65 18 hpf in l 1.65 100k w 19 mtx out l 1.65 20 mtx in l 1.65 b 21 inv out l 1.65 22 inv in l 1.65 100k w 23 pre out l 1.65 24 mode 24 25k w 25 ext in l 1.65 75k w 26 bg 1.25 10k w 27 int in l 1.65 75k w 28 gnd 29 vreg 2.5 c 30 int in r 1.65 75k w 31 ripl 1.65 50k w 32 ext in r 1.65 75k w ef (p - p) ef (p - p) ef (p - p) c (p - p) ef (p - p) ef (p - p) ef (p - p) c (p - p) ef (p - p) ef (p - p) ef (p - p) pin name function pin no. voltage ( v) * ef: emitter follower, p-p: push pull, b: base, and c: collector. circuit mode control 1 input preamplifier output inverter input inverter output matrix amplifier input matrix amplifier output high-pass filter input signal output external microphone monaural decision signal output mix output low-pass filter block inverter input low-pass filter block inverter output v cc bias voltage detector circuit input detector circuit output signal output high-pass filter input matrix amplifier output matrix amplifier input inverter output inverter input preamplifier output mode control 24 input external microphone input for regulator ripple filter capacitor internal microphone input gnd regulator output internal microphone input for bias ripple filter capacitor external microphone input all numerical values are standardized values. pin descriptions
4 video ics BA7781k measurement circuit 2 1 3 4 5 6 7 8 24 23 22 21 20 19 18 17 16 15 14 13 11 10 9 25 27 28 29 30 31 32 ext int 13db 13db gnd reg bias int ext + ? nor wnd nor wnd 15db + ? ext ext bias v cc mix + ? 10db 15db ? + det 0.1 m 10k 10.5k 0.1 m 0.1 m 12 12 2200p 0.1 m 0.1 m 0.1 m 2200p sw2 hpf in 2.2 m + 1m 0.1 m 0.1 m 200k 200k 10 m + 10k 10.5k 1 2 mode 24 sw1 mode 1 hpf in l out v cc inv (11) in r out ext in int in int in ext in gnd 0.1 m 10 m 0.1 m 30k 0.1 m 10 m 0.1 m lch rch + + units resistor: w capacitor: f 26 12 fig. 1
5 video ics BA7781k application example 12 ext int 13db 13db gnd reg bias int ext + ? nor wnd nor wnd 15db + ext ext bias v cc mix + ? 10db 15db ? + det 0.1 m 10k 10.5k 100k 0.1 m 0.022 m 2200p 0.1 m 0.1 m 2200p 2.2 m + 1m 100k 220k 150k 10 m + 1 m + 10k 10.5k 100k a b l out v cc mic-mono r out ext in int in int in ext in 0.1 m 10 m 0.1 m 0.1 m 10 m 0.1 m + + 0.022 m 24k 15k 15k a' b' 2200p 0.01 m 0.01 m 24k 0.022 m 0.022 m gnd r ch l ch units resistor: w capacitor: f additional components int / ext monitoring int / ext l open 100k 29 1 2 3 4 5 24 23 22 21 20 19 18 17 16 13 12 11 10 9 26 27 28 30 31 32 67 25 15 8 14 100k * 1) when using the matrix circuit connect a-a' and b-b'. * 2) the pin 10 and 12 low-pass filter components are for fc = 150hz, gain = 0db, 18db / oct. ? fig. 2
6 video ics BA7781k measurement circuit switch table (blank cells: no spesification) sw1 sw2 mode1 mode24 11 h l 11 11 11 11 11 11 1 1 l l int 1 1 h l int 1 1 l l ext 11 1 1 h vth 1 1 vth l 2 2 h l inv (11) , hpf 1 1 h l inv (11) , int 11 h l 2 2 h l hpf, 16pin of vth inv, 16pin of vth int, ext int, ext ext int signal input pin parameter current dissipation 1 current dissipation 2 preamplifier gain output amplifier gain distortion maximum output output noise voltage input switch separation (int ? ext) interchannel separation internal microphone power supply voltage input switch control voltage high-pass filter switching attenuation characteristic high-pass filter control voltage conditions other than no. 1 * h and l are v cc and gnd levels. measure the voltage range that maintains the mode for vth. operation notes (1) automatic wind-noise rejection circuit the max out (pin 10) signal passes through the three-stage low-pass filter connected between pins 10 and 12, and the dc level of the low-frequency signal component is detected. this dc voltage (pin 16 dc voltage) automatically controls the on / off switching of the high-pass filter. the components connected to pins 11 and 12 set the gain of a multiple-feedback-type two- stage low-pass filter constructed around an inverting amplifier, and by changing the gain of the circuit you can adjust the detection sensitivity. it is also possible to switch the high-pass filter manually by applying a dc voltage to pin 16 (see fig 2). (2) additional compornents for int / ext monitor use an internal circuit sets pin 12 to roughly the bias poten- tial in int mode, and to gnd for ext mode. this switches the external transistor on and off for int and ext modes respectively. this can be used to indicate whether the microphone amplifier is operating with the int or ext input. in the case of a camcorder, this can be used to display a massage such as ?xt mic on in the evf.
7 video ics BA7781k electrical characteristic curves output level: v rout ( dbv) 15pin input signal level: v detin ( dbv) v cc = 3.3v ta = 25 c ?6 0 ?4 0 ?2 0 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 ?1 0 input: 80hz nor side output 6 ? 8pin hpf side output 7 ? 8pin fig. 3 hpf switching characteristics 16pin detect output: v detout ( v) 15pin input signal level: v detin ( dbv) v cc = 3.3v ta = 25 c 0 0.5 1.0 1.5 2.0 2.5 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 ?1 0 input: 80hz fig. 4 detector voltage characteristis external dimensions (units: mm) 0.15 0.4 0.1 24 17 16 9 8 1 25 32 7.0 0.2 9.0 0.3 7.0 0.2 9.0 0.3 0.4 0.05 1.45 0.1 0.15 0.1 0.8 qfp32
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